Photoelectric conversion device and driving method therefor

ABSTRACT

In a photoelectric conversion device for reading signals in succession from plural photoelectric converting elements (S11-S33), arranged two-dimensionally on a substrate, by successively scanning drive lines (g1-g3) in the X-direction thereby transferring signals charges along signal lines in the Y-direction, for reading the signals of the photoelectric converting elements in a partial area, only the arbitrarily selected drive lines for the plural photoelectric converting elements are scanned in succession while the remaining drive lines are not driven or are driven simultaneously for transferring the charges at a timing different from the timing of drive of the arbitrarily selected drive lines.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion device and adriving method therefor, and more particularly to a photoelectricconversion device provided with a two-dimensional array of readingpixels, adapted for use in a facsimile apparatus, a digital copyingapparatus of an X-ray image capture device, and a driving methodtherefor.

2. Related Background Art

An image reading system utilizing a reduction optical system and a CCDsensor has been conventionally employed for the image capture in thefacsimile apparatus, digital copying apparatus or X-ray image capturedevice, but, based on the recent development of photoelectricsemiconductor materials exemplified by hydrogenated amorphous silicon(hereinafter referred to as a-Si), there are conducted activedevelopments for so-called contact sensors having photoelectricconverting elements and signal processing units on a large-sizedsubstrate to enable image reading with an optical system of a size sameas that of the information source. Particularly a-Si, being usable notonly as a photoelectric converting material but also in a thin filmfield effect transistor (hereinafter written as TFT), provides anadvantage that the photoelectric converting semiconductor layer and thesemiconductor layer of TFT can be formed simultaneously.

However, in such photoelectric conversion devices, in case of reading apartial area (hereinafter called trimming operation), it is required todrive all the drive lines or all the pixels to read the outputs of allthe pixels and then to extract the signals corresponding to the certainrequired area. For this reason there is encountered a drawback ofrequiring time for driving the unnecessary drive lines and time forreading the unnecessary output signals.

In case the photoelectric conversion device is of a large area withpixels of a high definition as in the X-ray image capture device,particularly in case of capturing information of a large number ofpixels of a high definition as so-called moving image as in the case ofobserving the image while irradiating the X-ray image capture devicecontinuously with X-rays, such drawback becomes serious because of thesignificant signal processing time and also because of the increasedX-ray radiation dose in case of the X-ray image capture.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a photoelectricconversion device including a two-dimensional array of pluralphotoelectric converting elements, capable of high-speed signal reading,and a driving method therefor.

Another object of the present invention is to provide a photoelectricconversion device, including an array of plural photoelectric convertingelements, not requiring time for driving the unnecessary drive lines andtime for reading unnecessary output signals in case of reading thesignals of the photoelectric converting elements of a partial area (suchreading operation being hereinafter called a trimming operation).

Still another object of the present invention is to provide aphotoelectric conversion device enabling image reading with a highersensitivity, usable as an X-ray image capture device with a reducedX-ray radiation dose, and a drive method therefor.

Still another object of the present invention is to provide a drivemethod for a photoelectric conversion device in which signals of pluralphotoelectric converting elements arranged in a two-dimensional array ona substrate are successively read by scanning the drive lines inX-direction in succession and transferring the signal charges in thesignal lines in the Y-direction, wherein the signal charge transfer isexecuted by scanning in succession only arbitrarily selected drive linesamong those for the plural photoelectric converting elements, while notdriving the remaining drive lines for the signal charge transfer ordriving the remaining plural drive lines simultaneously at a timingdifferent from that for the above-mentioned arbitrary drive lines.

Still another object of the present invention is to provide a drivemethod for such photoelectric conversion device, wherein potentials atboth ends of each of the photoelectric converting elements in theremaining drive lines are simultaneously returned to an initial value.

Still another object of the present invention is to provide a drivemethod for such photoelectric conversion device, wherein such remainingdrive lines are driven either collectively or in a divided manner.

Still another object of the present invention is to provide a drivemethod for such photoelectric conversion device, wherein the drive linesexecute a drive for initializing all the photoelectric convertingelements after the aforementioned arbitrary drive lines execute transferof the signal charges obtained by the photoelectric conversion in thecorresponding photoelectric converting elements.

Still another object of the present invention is to provide a drivemethod having a mode for reading the signals by driving theaforementioned arbitrary drive lines and another mode for reading thesignals by driving second arbitrary drive lines different from theabove-mentioned arbitrary drive lines, and a drive method in which theabove-mentioned two modes are executed alternately.

Still another object of the present invention is to provide a drivemethod wherein the aforementioned arbitrary drive lines are selected ina plural number and such selected drive lines are driven in successionfrom the innermost one toward the outermost one, and/or theaforementioned arbitrary drive lines are selected in a plural number anda drive is executed for initializing the selected drive lines insuccession from the innermost one toward the outermost one prior to thereading of the signal charges by the drive lines.

Still another object of the present invention is to provide a drivemethod for reading image data from a photoelectric conversion deviceincluding a photodetector array consisting of a matrix array ofphotosensor elements, comprising the steps of:

a) determining, as an object area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photodetector array;

b) detecting the signals of the photosensor elements of at least a row,from the side of one of the mutually opposed edges, in the direction ofrow, of the object area;

c) detecting the signals of the photosensor elements of at least a row,from the side of the other of the mutually opposed edges, in thedirection of row, of the object area; and

d) alternately repeating the steps b) and c), except for the alreadydetected rows, until the signals of the photosensor elements of the rowat the central portion of the object area are detected.

Still another object of the present invention is to provide a drivemethod for reading image data from a photoelectric conversion deviceincluding a photodetector array consisting of a matrix array ofphotosensor elements, comprising the steps of:

a) determining, as an object area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photodetector array;

b) detecting signals of the photosensor elements of at least a row in acentral portion of the object area;

c) detecting signals of the photosensor elements of at least a rowadjacent to one of the two sides of the already detected row;

d) detecting signals of the photosensor elements of at least a rowadjacent to the other of the two sides of the already detected row; and

e) alternately repeating the steps of c) and d), except for the alreadydetected rows, until the signals of the photosensor elements of the rowson the mutually opposed edges, in the direction of row, of the objectarea are detected.

Still another object of the present invention is to provide a drivemethod for driving a photoelectric conversion device which is providedwith a photodetector array consisting of a matrix array of photosensorelements and in which signals from at least a part of the photosensorelements of each column are taken out from a common column output linethrough switching elements, comprising the steps of:

a) determining, as an object area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photodetector array;

b) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row,from the side of one of the mutually opposed edges, in the direction ofrow, of the object area;

c) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row,from the side of the other of the mutually opposed edges, in thedirection of row, of the object area; and

d) alternately repeating the steps b) and c), except for the alreadydetected rows, until the signals of the photosensor elements of the rowat the central portion of the object area are detected.

Still another object of the present invention is to provide a drivemethod for driving a photoelectric conversion device which is providedwith a photodetector array consisting of a matrix array of photosensorelements and in which signals from at least a part of the photosensorelements of each column are taken out from a common column output linethrough switching elements, comprising the steps of:

a) determining, as an object area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photodetector array;

b) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row atthe central portion of the object area;

c) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a rowadjacent to one of the side of the already detected row;

d) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a rowadjacent to the other of the side of the already detected row; and

e) alternately repeating the steps c) and d), except for the alreadydetected rows, until the switch elements corresponding to thephotosensor elements of the rows at the mutually opposed edges, in thedirection of row, of the object area are driven.

Still another object of the present invention is to provide aphotoelectric conversion device provided with a photodetector arraycomposed of a matrix array of photosensor elements and including asignal charge accumulation unit corresponding to each photosensorelement and a switch unit provided in the signal output path from suchsignal charge accumulation unit, the device comprising:

object area determination means for determining, as an object area ofthe user, an area of the photosensor elements defined by a desired rangeof rows and a desired range of columns in the photodetector array, anddrive means for generating a drive signal for the photodetector arraybased on the output of the object area determination means;

wherein the drive means is adapted to generate the drive signal for thephotodetector array in such a manner as to reset the charges of thesignal charge accumulation units by driving the switch units of thephotodetector array in succession from a row at the periphery of theobject area to a row at the center thereof, and, after the exposure tothe light, to read the signal charges of the signal charge accumulationunits by driving the switch units of the photodetector array insuccession from the central portion of the object area to the peripheralportion thereof.

Still another object of the present invention is to provide aphotoelectric conversion device comprising read instruction detectingmeans for detecting a read instruction, and control means forcontrolling the aforementioned drive means based on the output of theread instruction detecting means, wherein the control means is adaptedto effect the resetting, the exposure after the resetting and the signalcharge reading after the exposure based on the output of the readinstruction detecting means, and to provide a photoelectric conversiondevice further comprising conversion means for converting an X-ray,emitted from X-ray irradiation means, into a visible light, and adaptedto detect the visible light, emitted from the conversion means, by thephotodetector array.

Still another object of the present invention is to provide aphotoelectric conversion device, wherein the drive means is adapted togenerate drive signals for the photodetector array, in such a manner asto refresh the signal charge accumulation units by driving the switchunits of the photodetector array in succession from a row in theperipheral portion of the object area to a row at the central portionthereof.

Still another object of the present invention is to provide aphotoelectric conversion device for reading the signals in successionfrom plural photoelectric converting elements arranged two-dimensionallyon a substrate, by scanning the drive lines of the X-direction insuccession thereby transferring the signal charges in the Y-direction,comprising means for successively scanning the arbitrary drive linesonly of the above-mentioned plural photoelectric converting elements.

Still another object of the present invention is to provide suchphotoelectric conversion device comprising means for simultaneouslydriving the remaining drive lines at a timing different from the drivetiming for the above-mentioned arbitrary drive lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views of examples of thephotoelectric converting element, while FIG. 1C is an equivalent circuitdiagram showing a schematic drive circuit for the photoelectricconverting element shown in FIG. 1A or 1B;

FIG. 2 is a schematic cross-sectional view of a TFT (thin filmtransistor);

FIG. 3 is a chart showing an example of the relationship between thethickness of the gate insulation film of TFT and the yield;

FIG. 4 is a schematic circuit diagram of a photoelectric conversiondevice having a two-dimensional array of photoelectric convertingelements;

FIG. 5A is a schematic plan view of a pixel of the photoelectricconversion device, while FIG. 5B is a schematic cross-sectional view ofthe pixel shown in FIG. 5A;

FIG. 6 is a timing chart showing an example of drive of thephotoelectric conversion device shown in FIG. 4;

FIGS. 7 and 8 are schematic plan views showing examples of thearrangement of reading areas and driving IC's;

FIG. 9 is a schematic equivalent circuit diagram of an example of thephotoelectric conversion device;

FIGS. 10 and 11 are timing charts showing examples of drive of thephotoelectric conversion device shown in FIG. 9;

FIG. 12 is a schematic view showing the system configuration of an X-rayphotographing system utilizing a two-dimensional photoelectricconversion device;

FIG. 13 is a schematic plan view of a pixel structure of thephotoelectric converting element;

FIG. 14 is a schematic cross-sectional view of an example of the pixelstructure of the photoelectric converting element;

FIGS. 15A, 15B and 15C are schematic energy band charts showing anexample of the function of the photoelectric converting element;

FIG. 16 is a schematic equivalent circuit diagram of an example of driveof a photoelectric converting element;

FIG. 17 is a timing chart showing an example of drive of thephotoelectric conversion device;

FIG. 18 is a schematic equivalent circuit diagram of an example of driveof a photoelectric converting element;

FIG. 19 is a timing chart showing an example of drive of thephotoelectric conversion device;

FIG. 20 is a schematic view showing the system configuration of anexample of selection of an object area; and

FIG. 21 is a view showing the concept of the object area.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

At first there will be explained an example of the photosensor elementin which the present invention is applicable.

FIGS. 1A to 1C are views showing the configuration of the photosensor,wherein FIGS. 1A and 1B show layer structures of two kinds ofphotosensor while FIG. 1C shows a representative driving method commonto two kinds. FIGS. 1A and 1B both show photosensors of photodiode type,respectively called PIN type and Shottky type, wherein shown are asubstrate 1 which is insulating at least at the surface thereof; a lowerelectrode 2; a p-type semiconductor layer 3 (hereinafter calledp-layer); an intrinsic semiconductor layer 4 (hereinafter calledi-layer); an n-type semiconductor layer 5 (hereinafter called n-layer);and a transparent electrode 6. In the Shottky type structure, thematerial of the lower electrode 2 is suitably selected to form a Shottkybarrier layer for inhibiting electron injection from the lower electrode2 to the i-layer 4. In FIG. 1C, there are shown a photosensor 10represented as a symbol; a power source 11 and a detecting unit 12 suchas a current amplifier. In the photosensor 10, C indicates the side ofthe transparent electrode 6 shown in FIGS. 1A and 1B, while A indicatesthe side of the lower electrode 2, and the power source 11 is soarranged as to apply a positive voltage to the side A with respect tothe side C.

Now the function of the photosensor will be briefly explained. As shownin FIGS. 1A and 1B, when the light enters from a direction indicated byan arrow and reaches the i-layer 4, it is absorbed to generate anelectron and a hole. Since an electric field is applied to the i-layer 4by the power source 11, the electron moves toward the side C, throughthe n-layer 5 to the transparent electrode 6, while the hole movestoward the side A, or to the lower electrode 2. In this manner aphotocurrent is generated in the photosensor 10. In the absence of thelight entry, the i-layer 4 does not generate electron or A hole. Alsothe n-layer 5 functions as a hole injection inhibiting layer for theholes in the transparent electrode 6, while the p-layer 3 in the PINtype shown in FIG. 1A or the Shottky barrier layer in the Shottky typeshown in FIG. 1B functions as an electron injection inhibiting layer forthe electrons in the lower electrode 2, so that no current is generated.Consequently the presence or absence of incident light causes avariation in the current, and a photosensor can be obtained by detectingsuch variation by the detecting unit 12 shown in FIG. 1C.

However it is not easy to construct a photoelectric conversion device ofa sufficiently high S/N ratio and a low cost with the photosensors ofthe above-explained configurations, because of the following reasons.The first reason is the necessity of injection inhibiting layers in twopositions, but in the PIN type shown in FIG. 1A and in the Shottky typein FIG. 1B. In the PIN type shown in FIG. 1A, the n-layer 5 constitutingthe injection inhibiting layer is required to have the properties ofguiding the electrons to the transparent electrode 6 and inhibiting theinjection of the holes into the i-layer 4. If either of these propertiesis not satisfied, there will result a decrease in the S/N ratio becausethe photocurrent decreases or because the current in the absence of theincident light (hereinafter called "dark current") is generated orincreases. Such dark current is itself considered as a noise and alsocontains therein a fluctuation, called shot noise or so-called quantumnoise, and the quantum noise involved in the dark current cannot be madesmaller even by the subtraction of the dark current in the detectionunit 12. For improving these properties, it is usually necessary tooptimize the film forming conditions for the i-layer 4 and the n-layer 5or the annealing condition after the film formation. However, also thep-layer 3 constituting the other injection inhibiting layer is requiredto have properties similar to the foregoing but inversely applicable tothe electrons and the holes. Usually the condition for optimizing then-layer is not same as that for optimizing the p-layer, and it is noteasy to satisfy both conditions at the same time. Stated differently,the formation of the photosensor of a high S/N ratio becomes difficultbecause of the necessity of two injection inhibiting layers of mutuallyopposed properties within a same photosensor. This applies also to theShottky type photosensor shown in FIG. 1B. Also such Shottky typephotosensor shown in FIG. 1B employs, in one of the injection inhibitinglayers, a Shottky barrier layer, relying on the difference in the workfunctions of the lower electrode 2 and the i-layer 4, whereby thematerial of the lower electrode 2 is limited or the characteristics aresignificantly influenced by the presence of the localized level at theinterface. It is therefore not easy to ideally satisfy all theseconditions. It is also proposed, for improving the property of theShottky barrier layer, to form a silicon film or a metal oxide ornitride film of a small thickness in the order of 100 Å between thelower electrode 2 and the i-layer 4, for improving the effects ofguiding the holes to the lower electrode 2 and inhibiting the injectionof the electrons into the i-layer 4 by the tunneling effect. Suchconfiguration also utilizes the difference of the work functions andinevitably involves the limitation on the material of the lowerelectrode 2. Also in order to achieve mutually opposite properties,namely the inhibition of injection of the electrons and the promotion ofmovement of the holes by the tunneling effect, the thickness of suchoxide or nitride film is limited to a very small value, in the order of100 Å, and it is not easy to achieve a high productivity because of thedifficult in the control of thickness or film quality.

Also the necessity for the injection inhibiting layers in two positionslowers the productivity, thus giving rise to an increased cost, becausethe performance as the photosensor cannot be obtained if a defect isgenerated, for example by particles, even in one of the two injectioninhibiting layers, which play important role in the performance.

Such second reason will be explained with reference to FIG. 2, whichshows the layered configuration of a field effect transistor consistingof thin semiconductor films (TFT). Such TFT is often utilized as a partof the control unit in the photoelectric conversion device. In FIG. 2,components same as those in FIGS. 1A to 1C are represented by samenumbers. In FIG. 2 there are also shown is a gate insulation film 7, andan upper electrode 60. Such TFT is prepared in the following manner. Onan insulating substrate 1, there are formed in succession a lowerelectrode 2 functioning as a gate electrode (G), a gate insulation film7, an i-layer 4, an n-layer 5, and an upper electrode 60 functioning assource and drain electrodes (S, D). Then the upper electrode 60 isetched to form the source and drain electrodes, and then the n-layer 5is etched to form a channel portion. As the characteristics of the TFTare sensitive to the state of the interface between the gate insulationfilm 7 and the i-layer 4, these films are normally deposited insuccession under a same vacuum condition, in order to avoidcontamination of these films.

In case a photosensor is formed also on the substrate of the TFT, theabove-explained layer structure becomes the cause of increased cost ordeteriorated characteristics. More specifically, the photosensor has alayer structure, in the order from the substrate side, ofelectrode/p-layer/i-layer/n-layer/electrode in case of the PIN typeshown in FIG. 1A or electrode/i-layer/n-layer/electrode in case of theShottky type shown in FIG. 1B, while the TFT has a layer structure, inthe order from the substrate side, of electrode/insulationfilm/i-layer/n-layer/electrode, and these structures cannot be preparedin a same process sequence without causing a loss in the productionyield or an increase in cost because of the complication of the process.Also the formation of i-layer/n-layer at the same time in a commonprocess requires an etching step for the gate insulation film 7 and thep-layer 3, and, in such case, these results possibility that theinjection inhibiting p-layer 3, important in the performance of thephotosensor, and the i-layer 4 cannot be formed in succession under asame vacuum condition or that the interface between the gate insulationfilm 7, important in the TFT, and the i-layer 4 is contaminated byetching operation for patterning the gate insulation film, eventuallyleading to a deterioration in the characteristics and in the S/N ratio.

The layered configuration can be made same in case an oxide or nitridefilm is formed between the lower electrode 2 and the i-layer 4 forimproving the characteristics of the Shottky type photosensor shown inFIG. 1B. However such oxide or nitride film is required to have athickness in the order of 100 Å and cannot therefore be used in commonwith the gate insulation film. FIG. 3 shows an experimental result ofthe present inventors on the relationship between the thickness of thegate insulation film and the production yield of the TFT. The productionyield became drastically lower when the thickness of the gate insulationfilm was reduced from 1000 Å, and was reduced to about 30% and 0%respectively at thicknesses of 800 Å and 500 Å, and even the function ofTFT could not be observed at a thickness of 250 Å. These data indicatethat the oxide or nitride film for the photosensor utilizing thetunneling effect cannot be used as the gate insulation film, which hasto perform insulation for the electrons or the holes, in the TFT.

It is also difficult to prepare a capacitance element (hereinaftercalled "capacitor"), which is unrepresented but required for obtainingan integrated value of the charge or the current, with a satisfactoryperformance of a low leakage, in the configuration same as that of thephotosensor. This is because, while the capacitor always requires alayer for inhibiting the movement of electrons and holes as anintermediate layer for two electrodes in order to accumulate a chargetherebetween, it is difficult to obtain such intermediate layer ofsatisfactory performance with low thermal leakage as the photosensoronly contains semiconductor layers or layers allowing the movement ofelectrons or holes between the electrodes.

Such lack of matching in process or in performance with the TFT or thecapacitor which is an important element in the structure of thephotoelectric conversion device renders it difficult to improve theproduction yield in constructing a system containing a two-dimensionalarray of a plurality of photosensors and designed to detect the signalsthereof in succession, because of the large number and complexity of theprocess steps, and is considered a significant drawback in realizing ahigh-performance device of multiple functions with a low cost.

In the following there will be explained a prior photoelectricconversion device provided with a photosensor proposed to resolve theabove-mentioned difficulties.

FIG. 4 is an entire circuit diagram of a prior example of thephotoelectric conversion device, FIG. 5A is a schematic plan view of anexample of a component element corresponding to a pixel of thephotoelectric conversion device, and FIG. 5B is a schematiccross-sectional view along a line 5B--5B in FIG. 5A. In FIG. 4, thereare shown photoelectric converting elements S11-S33 in which the lowerelectrode side and the upper electrode side are respectively indicatedby G and D; accumulating capacitors C11-C33; transfer TFT's T11-T33; areading power source Vs and a refreshing power source Vg connected,respective through switches SWs, SWg, to the G electrodes of al thephotoelectric converting elements S11-S33. The switch SWs is connectedthrough an inverter to a refreshing control circuit high frequency,while the switch SWg is connected directly thereto, and these switchesare so controlled that the switch SWg is turned on during the refreshingperiod. A pixel is composed of a photoelectric converting element, acapacitor and a TFT, and the output signal therefrom is supplied,through a signal line SIG to a detecting integrated circuit IC. In suchphotoelectric conversion device, nine pixels are divided into threeblocks, and the outputs of three pixels in each block are simultaneouslytransferred to the signal line SIG to the detecting integrated circuitIC and are converted thereinto into successive outputs (Vout). The threepixels in each block are arranged horizontally while the three blocksare arranged vertically to obtain a two-dimensional array of the pixels.

In FIG. 4, an area surrounded by a broken-lined frame is formed on asame insulating substrate of a large area, and a portion thereofcorresponding to a first pixel is shown in a schematic plan view in FIG.5A. Also FIG. 5B is a schematic cross-sectional view corresponding to aline 5B--5B. In these drawings there are shown a photoelectricconverting element S11, a TFT T11, a capacitor C11, and a signal lineSIG. In such prior photoelectric conversion device, proposed by thepresent inventor before, the capacitor C11 and the photoelectricconverting element S11 are not particularly isolated but the electrodesof the photoelectric converting element S11 are made larger toconstitute the capacitor C11. Such configuration is enabled by a factthat the photoelectric converting element and the capacitor have a samelayer structure and features such prior proposed photoelectricconversion device. On the pixel there are formed a passivation siliconnitride film SiN and a fluorescent member CsI composed for example ofcesium fluoride. The X-ray entering from above is converted by thefluorescent member CsI into light (represented by broken-lined arrows),which enters the photoelectric converting element.

In the following there will be explained the function of theabove-explained photoelectric converting device with reference to FIG. 4and FIG. 6, which is a timing chart showing an example of the functionof the circuit shown in FIG. 4.

At first a Hi-level signal is applied, by shift registers SR1, SR2, tocontrol lines g1-g3, s1-s3, whereby the transfer TFT's T11-T33 andswitches M1-M3 are turned on and rendered conductive to shift the Delectrodes of all the photoelectric converting elements S11-S33 to theground potential as the input terminal of an integrating detector Amp isdesigned at the ground potential. At the same time the refresh controlcircuit high frequency releases a Hi-level signal to turn on the switchSWg, whereby the G electrodes of all the photoelectric convertingelements S11-S33 are shifted to a positive potential by the refreshingpower source Vg and all the photoelectric converting elements S11-S33assume the refreshing mode and are refreshed. Then the refresh controlcircuit high frequency releases an Lo-level signal to turn on the switchSWs, whereby the G electrodes of all the photoelectric convertingelements S11-S33 are shifted to a negative potential by the readingpower source Vs. Thus all the photoelectric converting elements S11-S33assume the photoelectric conversion mode, and the capacitors C11-C33 areinitialized at the same time. In this state the shift registers SR1, SR2send Lo-level signals to the control lines g1-g3, s1-s3 to turn offswitches M1-M3 of the transfer TFT's T11-T33, whereby the D electrodesof all the photoelectric converting elements S11-S33 are left open in DCmanner but are retained at a certain potential by the capacitorsC11-C33. At this point, however, the photoelectric converting elementsS11-S33 do not receive light and does not generate photocurrents,because of absence of entry of the X-ray. Then, the X-ray is emitted inpulsed manner, transmitted for example by a human body and enters thefluorescent member CsI for conversion into light, which enters therespective photoelectric converting elements S11-S33. Such incidentlight contains information on the internal structure for example of thehuman body. The photocurrents generated by the incident light areaccumulated in the capacitors C11-C33, in a form of charges, which areretained even after the X-ray irradiation is terminated. Then the shiftregister SR1 applies a Hi-level control pulse to the control line g1while the shift register SR2 applies control pulses to the control liness1-s3 whereby output signals v1-v3 are released in succession throughthe switches M1-M3 of the transfer TFT's T11-T33. Also other signals arereleased in succession by similar control of the shift registers SR1,SR2, whereby the two-dimensional information of the internal structureof the human body is obtained as v1-v9. A still image is obtained by theprocess explained in the foregoing, but such process is repeated toobtain a moving image.

In the above-explained photoelectric conversion device, the G electrodesof the photoelectric converting elements are connected in common and arecontrolled at the potential of the refreshing power source Vg or of thereading power source Vs through the switches SWg and SWs, so that allthe photoelectric converting elements can be simultaneously switched tothe refreshing mode or the photoelectric conversion mode. It is thusrendered possible to obtain a light output signal, by a TFT per pixel,without complex control.

In the above-explained photoelectric conversion device, nine pixels aretwo-dimensionally arranged in a 3×3 matrix and are transferred andoutputted in three divided operations. Such configuration can beexpanded, for example, to a two-dimensional array of 2000×2000 pixels,arranged with a density of 5×5 pixels per square millimeter to obtain anX-ray detector of 40×40 cm. Such X-ray detector can be combined, inplace for an X-ray film, with an X-ray generator to form an X-ray imagecapture apparatus that can be used for chest radiological inspection,mammographic inspection or non-destructive testing. In contrast to theconventional X-ray film, such apparatus allows to instantaneouslydisplay the output image on an output device such as a CRT, and also toconvert the output signals into digital form and to effect suitableimage processing on a computer. Also such image can be stored on amagnetooptical disk and the images taken in the past can be retrievedinstantaneously. Also such apparatus has a sensitivity superior to thatof the X-ray film and can be obtain a clear image with a weak X-rayhaving less detrimental effect on the human body.

FIGS. 7 and 8 show an example of the photoelectric conversion devicehaving 2000×2000 pixels. Such detector with 2000×2000 pixels can beobtained by increasing the number of the elements, in the broken-linedframe shown in FIG. 4, in the vertical and horizontal directions. Insuch case, there will be required 2000 control lines g1-g2000 and 2000signal lines sig1-sig2000. Also the shift register SR1 or the detectingintegrated circuit IC becomes large in scale as it has to control orprocess 2000 lines. Such device, if formed as a single chip, becomesextremely large and is disadvantageous in the projection yield or in thecost. Therefore the shift register SR1 is constituted by 20 chipsSR1-1-SR1-20, each covering 100 lines. Also the detecting integratedcircuit is constituted by 20 chips IC1-IC20, each covering 100processing circuits.

In the configuration shown in FIG. 7, 20 chips (SR1-1-SR1-20) aremounted at the left side (L) while 20 chips are mounted at the lowerside (D), and 100 control or signal lines are connected by wire bondingto each chip. In FIG. 7, a broken-lined frame area corresponds to thatin FIG. 4. Omitted from the illustration are the connections to theexterior and other components such as SWg, SWs, Vg, Vs, RF etc. Thedetecting integrated circuits IC1-IC20 have 20 outputs (Vout) which maybe combined into one for example through a switch or may be released tothe exterior in parallel manner.

FIG. 8 shows another configuration, having 10 chips SR1-1-SR1-10 at theleft side (L), 10 chips SR1-11-SR1-20 at the right side (R), 10 chipsIC1-IC10 at the upper side (U) and 10 chips IC11-IC20 at the lower side(D). This configuration can improve the production yield, since thelines are equally divided by 1000 lines to each of the upper, lower,left and right sides whereby the density of the lines or of the wirebonding on each side can be reduced. The division of the lines is madein such a manner that the odd-numbered control lines g1, g3, g5, . . . ,g1999 are extracted to the left side L while the even-numbered controllines are extracted to the right side R, whereby the lines can beextracted at a constant pitch, without concentration in density. Thelines to the upper side and to the lower side can also be divided in asimilar manner.

In another unillustrated arrangement, the control lines are divided ingroups of lines which are continuous for each chip, namely g1-g100,g201-g300, . . . , g1801-g1900 at the left side L and g101-g200,g301-g400, . . . , g1901-g2000 at the right side R, alternately to theleft and right sides. Such arrangement allows continuous control withsimpler control of drive timing within each chip, which can be made lessexpensive because of the simpler circuit configuration. A similararrangement can be adopted also in the upper and lower sides to enablecontinuous processing, thereby allowing the use of inexpensive circuits.

The configuration shown in FIGS. 7 or 8 can be obtained by forming thecircuits of the broken-lined frame area on a large substrate and thenmounting the chips on such substrate, or by mounting a substrate bearingthe circuits of the broken-lined frame area and the chips on anotherlarge substrate. It is also possible to mount the chips on a flexiblesubstrate and to adhere and connect it to a substrate bearing thecircuits of the broken-lined frame area.

Such large-area photoelectric conversion device with a large number ofpixels can be obtained with a high production yield and a low cost, byforming the different elements simultaneously with common films, thuswith a simpler process with a reduced number of process steps. Also thecapacitor the TFT and the photoelectric converting element can be formedwithin a same pixel, whereby the number of the elements can be reducedalmost to a half and the production yield can thus be improved further.

In the above-explained configuration, the photoelectric convertingelement employed therein can detect the amount of the incident lightwith only one injection inhibiting layer and enables easy optimizationof the production process, improvement in the production yield andreduction in the production cost, thus providing a photoelectricconversion device of a high S/N ratio and a low cost. Also as itslayered configuration of first electrode layer/insulationlayer/photoelectric converting semiconductor layer in succession on thesubstrate does not utilize the tunneling effect or the Shottky barrier,the materials constituting the electrodes can be arbitrarily selected,and a larger freedom is secured for the thickness of the insulationlayer and other controls.

Also such photoelectric converting element materials well with theswitching element such as thin-film field effect transistor (TFT) and/orthe capacitance element to be formed at the same time. These elements,having a same layered configuration, can be simultaneously formed bycommon films, and the films important for the photoelectric convertingelement and the TFT can be simultaneously formed under a same vacuumcondition. Also the photoelectric converting element can be obtainedwith a high S/N ratio and a lower cost. Furthermore the capacitor,containing an insulation layer in the intermediate layer, can beprovided with satisfactory performance. Thus there can be provided aphotoelectric conversion device of a high performance, capable ofoutputting the integrated values of the optical information obtainedwith the plural photoelectric converting elements with a simpleconfiguration. Also there can be provided a facsimile device or an X-rayimage capture device of a large area with high performance and a lowcost.

In any photoelectric conversion device having a two-dimensional array ofa plurality of photosensors (photoelectric converting elements), it isimportant to obtain the necessary information at a higher speed.

A method for meeting such requirement, in a photoelectric conversiondevice for reading the signals in succession from a two-dimensionalarray of plural photoelectric converting elements on a substrate, bysuccessively scanning plural drive lines in the X-direction therebytransferring the signal charges in the signal lines of the Y-direction,consists of successively scanning only arbitrarily selected drive linesof the above-mentioned photoelectric converting elements andsimultaneously driving the remaining drive lines at a timing differentfrom that for the above-mentioned arbitrarily selected drive lines,thereby transferring the signal lines.

Such method allows to eliminate the time required for driving theunnecessary drive lines and for reading the unnecessary output signalsby simultaneously driving the unnecessary drive lines instead ofsuccessive drive, whereby the signals of the necessary area can be readat a higher speed. Thus, in case the photoelectric conversion device isutilized as an X-ray image capture device, particularly in case ofobservation of a moving image by continuous irradiation of such imagecapture device with X-ray, there can be achieved a reduction in theX-ray radiation dose, providing a significant advantage in medical andenvironmental sense.

Also the sensor characteristics of all the photoelectric convertingelements can be equalized by simultaneously returning the potentials atboth ends of unnecessary photoelectric converting elements to theinitial value within a short time, whereby provided is a photoelectricconversion device with a high reliability in the obtained information.

Another method for meeting the aforementioned requirement, in aphotoelectric conversion device for reading the signals in successionfrom a two-dimensional array of plural photoelectric converting elementson a substrate, by successively scanning plural drive lines in theX-direction thereby transferring the signal charges in the signal linesof the Y-direction, consists of successively scanning in succession thearbitrarily selected necessary drive lines only, and not effecting thedrive of the remaining drive lines for the transfer of the signalcharges.

Also in such case, the time required for driving the unnecessary drivelines and for reading the unnecessary output signals can be eliminated,so that the signals of the necessary area can be read at a higher speed.Thus, as explained in the foregoing, in case the photoelectricconversion device is utilized as an X-ray image capture device,particularly in case of observation of a moving image by continuousirradiation of such image capture device with X-ray, there can beachieved a reduction in the X-ray radiation dose, providing asignificant advantage in medical and environmental sense.

In the X-ray image capture device, an X-ray beam emitted from an X-raysource is directed to an object (specimen) to be analyzed, such as amedical patient. There is also known a method, after the X-ray passesthrough the specimen, of converting the X-ray image into a visibleoptical image by an image intensifier, then preparing an analog videosignal from the visible optical image by a video camera and displayingsuch analog video signal on a monitor. In such case, since an analogvideo signal is prepared, the image processing for automatic luminancecontrol and image emphasis is conducted in the analog form.

On the other hand, in the above-explained solid-state X-ray detectorutilizes a two-dimensional array containing 3000 to 4000 detectingelements, such as photodiodes, in each line (such array beinghereinafter called "detecting element array" or "detector array"). Eachdetecting element prepares an electrical signal corresponding to thepixel luminance of the X-ray image projected onto the detector, and thesignals from the detecting elements are individually read and digitized,and are used for image processing, storage and display.

In such solid-state detecting element array, the bias charges set in thedetecting elements may be partially discharged by the current leakage inthe transistors or by a phenomenon generally called "dark current". Suchcharge depletion resulting from such dark current or leaking currentinduces an offset in the image signals. Since the amount of chargeseliminated by such currents is not constant, the offset in the signalsfluctuates, thus adding an uncertain factor to the outputs of thedetectors.

The amount of charges eliminated from the detecting elements by theabove-mentioned currents is a function of the time from the biasresetting of the detecting elements to the detection of the charges inthe detecting elements. Consequently, for minimizing the influence ofthese currents, it is desirable to minimize the time required for signalreading from the elements of the detecting element array. On the otherhand, for reducing the electrical noises added from the circuitry to thesignals of the detectors, it is desirable to reduce the frequency bandwidth of the image signal processing circuit and to extend the signalreading period.

In the photodetector array of matrix shape, the signals of the detectingelements are read one-directionally from one of the two sides mutuallyopposed in the direction of rows or columns to the other.

In most cases, however, the observer is interested in the central areaof the image capture area, so that it is desirable to obtain the highestimage quality in such central area. Also in a photodetector array ofhigh resolution, it is particularly desirable to improve the imagecapturing speed by capturing the image with the detecting elements ofthe above-mentioned interest area.

It is therefore preferable to enable the image data reading so as toreduce the deterioration in the image quality in the image portion inwhich the observer is most interested.

In reading the image data from a photoelectric conversion deviceincluding a matrix array of photosensor elements, a high image qualitycan be obtained in an interest area by a method comprising steps of:

a) determining, as an interest area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photoelectric conversion device;

b) detecting the signals of the photosensor elements of at least a row,from the side of one of the mutually opposed edges, in the direction ofrow, of the interest area;

c) detecting the signals of the photosensor elements of at least a row,from the side of the other of the mutually opposed edges, in thedirection of row, of the interest area; and

d) alternately repeating the steps b) and c), except for the alreadydetected rows, until the signals of the photosensor elements of the rowat the central portion of the interest area are detected.

Also in reading the image data from a photoelectric conversion deviceincluding a photosensor array in matrix form, there can be obtained ahigh image quality in the interest area by a method comprising steps of:

a) determining, as an interest area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photoelectric conversion device;

b) detecting signals of the photosensor elements of at least a row in acentral portion of the interest area;

c) detecting signals of the photosensor elements of at least a rowadjacent to one of the two sides of the already detected row;

d) detecting signals of the photosensor elements of at least a rowadjacent to the other of the two sides of the already detected row; and

e) alternately repeating the steps c) and d), except for the alreadydetected rows, until the signals of the photosensor elements of the rowson the mutually opposed edges, in the direction of row, of the interestarea are detected.

Also in driving a photoelectric conversion device which is provided witha matrix array of photosensor elements and in which signals from atleast a part of the photosensor elements of each column are taken outfrom a common column output line through switching elements, theinformation of the interest area can be obtained without deteriorationby another method comprising steps of:

a) determining, as an interest area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photoelectric conversion device;

b) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row,from the side of one of the mutually opposed edges, in the direction ofrow, of the interest area;

c) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row,from the side of the other of the mutually opposed edges, in thedirection of row, of the interest area; and

d) alternately repeating the steps b) and c), except for the alreadydetected rows, until the signals of the photosensor elements of the rowat the central portion of the interest area are detected.

Also in driving a photoelectric conversion device which is provided witha matrix array of photosensor elements and in which signals from atleast a part of the photosensor elements of each column are taken outfrom a common column output line through switching elements, theinformation of the interest area can be obtained with deterioration byanother method comprising steps of:

a) determining, as an interest area of the user, an area of thephotosensor elements defined by a desired range of rows and a desiredrange of columns in the photoelectric conversion device;

b) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a row atthe central portion of the interest area;

c) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a rowadjacent to one of the two sides of the already detected row;

d) taking out the signals to the column output line by driving a switchelement corresponding to the photosensor elements of at least a rowadjacent to the other of the sides of the already detected row; and

e) alternately repeating the steps c) and d), except for the alreadydetected rows, until the switch elements corresponding to thephotosensor elements of the rows at the mutually opposed edges, in thedirection of row, of the interest area are driven.

Also in a photoelectric conversion device provided with a matrix arrayof photosensor elements and including a signal charge accumulation unitcorresponding to each photosensor element and a switch unit provided inthe signal output path from such signal charge accumulation unit,satisfactory data reading in the interest area can be achieved by aphotoelectric conversion device comprising:

interest area determination means for determining, as an interest areaof the user, an area of the photosensor elements defined by a desiredrange of rows and a desired range of columns in the photoelectricconversion device, and drive means for generating a drive signal for thephotoelectric conversion device based on the output of the interest areadetermination means;

wherein the drive means is adapted to generate the drive signal for thephotodetector array in such a manner as to reset the charges of thesignal charge accumulation units by driving the switch units of thephotodetector array in succession from a row at the periphery of theinterest area to a row at the center thereof, and, after the exposure tothe light, to read the signal charges of the signal charge accumulationunits by driving the switch units of the photodetector array insuccession from the central portion of the interest area to theperipheral portion thereof.

The photoelectric conversion device may also be so constructed as tocomprise read instruction detecting means for detecting a readinstruction, and control means for controlling the aforementioned drivemeans based on the output of the read instruction detecting means,wherein the control means is adapted to control the drive means so as toeffect the resetting, the exposure after the resetting and the signalcharge reading after the exposure based on the output of the readinstruction detecting means.

The photoelectric conversion device may further comprise wavelengthconversion means for converting an X-ray, emitted from X-ray irradiationmeans, into a visible light, and adapted to detect the visible light,emitted from the conversion means, by the photodetector array.

The drive means may be so constructed as to generate drive signals forthe photodetector array, for refreshing the signal charge accumulationunits by driving the switch units of the photodetector array insuccession from a row in the peripheral portion of the interest area toa row at the central portion thereof.

In the following the present invention will be clarified in detail bypreferred embodiments thereof, with reference to the attached drawings.

[First embodiment]

FIG. 9 is a schematic circuit diagram of a photoelectric conversiondevice constituting a first embodiment of the present invention, andFIG. 10 is a timing chart showing an example of the function thereof.

Now the function of the first embodiment will be explained withreference to FIGS. 9 and 10.

At first a Hi-level signal is applied, by the shift registers SR1, SR2,to the control lines g1-g3, s1-s3, whereby the transfer TFT's T11-T33and the switches M1-M3 are turned on and rendered conductive to shiftthe D electrodes of all the photoelectric converting elements S11-S33 tothe ground potential as the input terminal of the integrating detectorAmp is designed at the ground potential.

At the same time the refresh control circuit high frequency releases aHi-level signal to turn on the switch SWg, whereby the G electrodes ofall the photoelectric converting elements S11-S33 are shifted to apositive potential by the refreshing power source Vg and all thephotoelectric converting elements S11-S33 assume the refreshing mode andare refreshed.

Then the refresh control circuit high frequency releases a Lo-levelsignal to turn on the switch SWs, whereby the G electrodes of all thephotoelectric converting elements S11-S33 are shifted to a negativepotential by the reading power source Vs. Thus all the photoelectricconverting elements S11-S33 assume the photoelectric conversion mode,and the capacitors C11-C33 are initialized at the same time. In thisstate the shift registers SR1, SR2 send Lo-level signals to the controllines g1-g3, s1-s3 to turn off the switches M1-M3 of the transfer TFT'sT11-T33, whereby the D electrodes of all the photoelectric convertingelements S11-S33 are left open in DC manner but are retained at acertain potential by the capacitors C11-C33.

At this point, however, the photoelectric converting elements S11-S33 donot receive light and does not generate photocurrents, because ofabsence of entry of the X-ray. Then the X-ray is emitted in pulsedmanner, transmitted for example by a human body and enters thefluorescent member CsI for conversion into light, which enters therespective photoelectric converting elements S11-S33. Such incidentlight contains information on the internal structure for example of thehuman body. The photocurrents generated by the incident light areaccumulated in the capacitors C11-C33, in a form of charges, which areretained even after the X-ray irradiation is terminated.

The function up to this point is same as that explained before. Howeverthe first embodiment is different in the driving method after thispoint, in case of a trimming drive in which the output signals arerequired only in a part of the photoelectric converting elements,instead of the signals of all the photoelectric converting elementsS11-S33.

In the following there will be explained, as an example, a case ofreading the output signals from the photoelectric converting elementsS21, S22 and S23 only.

As shown in FIG. 9, a control circuit A for controlling the shiftregisters SR1, SR2 sends an instruction for the control lines related tothe desired elements, namely the control lines g2 and s1-s3, whereby theshift register SR1 applies a Hi-level control pulse to the control lineg2 while the shift register SR2 applies Hi-level control pulses to thecontrol lines s1-s3 to release the signals s1-s3 in succession throughthe transfer TFT's T21-T23 and the switches M1-M3.

In this case, the control lines g1, g3 for transferring the unrequiredoutput signals of the photoelectric converting elements S11-S13 andS31-S33 are given Hi-level control pulses at the same time, after theapplication of the Hi-level pulse to the control line g2. In this mannerthe unnecessary signal charges can be transferred to restore the initialstate within a shorter time, in comparison with the driving method ofapplying the drive pulses in succession. More specifically, thepotentials at both ends of the unnecessary photoelectric convertingelements S11-S13 and S31-S33 are simultaneously returned to the initialvalue within a short time to equalize the sensor characteristics of allthe photoelectric converting elements S11-S33. As a result,photoelectrically converted information of high reliability can alwaysbe obtained, regardless of the state of the non-reading pixels.

Subsequently the shift register SR2 applies control pulses to thecontrol lines s1-s3 to release the signals v4-v6 through the switchesM1-M3, but such output signals v4-v6 are not particularly required.

Thus the required two-dimensional information for example of theinternal structure of the human body is obtained as v1-v3. A still imagecan be obtained by the process up to this point, but such process isrepeated for obtaining a moving image.

For enabling such control, the present embodiment is provided with acontrol circuit A for controlling the shift registers SR1 and SR2 asshown in FIG. 9. More specifically, the control circuit A generates asignal capable of starting the shift register SRI from an arbitraryaddress and stopping it at an arbitrarily designated address, and alsogenerates start and stop signals for determining the addresses and thenumber of repetition of the register SR2 according to the number ofdriven addresses of the register SR1. In this manner the output signalscan be obtained from the required photoelectric converting elements.Such control circuit, being capable of recognizing the entered bitnumbers of the sensors, is composed of logic circuits, but it may alsobe composed of circuits utilizing a microcomputer.

In the present embodiment there has been explained a case oftwo-dimensionally arranging nine pixels into a 3×3 matrix and outputtingthe signals of only three pixels therein, but the trimming can beachieved by driving, by the shift registers, any plural desired drivelines in succession.

In the present embodiment, in a photoelectric conversion device forreading in succession the signals from plural photoelectric convertingelements arranged in a two-dimensional array on a substrate, bysuccessively scanning the drive lines in the X-direction therebytransferring the signal charges in the signal lines in the Y-direction,the arbitrarily selected necessary drive lines alone are scanned insuccession while the remaining drive lines are not driven for thepurpose of signal charge transfer. Such photoelectric conversion device,capable of dispensing with the time required for driving the unnecessarydrive lines and for reading the unnecessary output signals, can read thenecessary signals at a higher speed.

Thus, in case the photoelectric conversion device is utilized as anX-ray image capture device, particularly in case of observation of amoving image by continuous irradiation of such image capture device withX-ray, there can be achieved a reduction in the X-ray radiation dose,providing medically and environmentally significant advantage, becausethe above-explained drive method practically corresponds to an increasein the sensitivity of the sensors, as the eliminated drive time can alsobe used for the exposure.

Also the sensor characteristics of all the photoelectric convertingelements can be equalized by simultaneously returning the potentials atboth ends of unnecessary photoelectric converting elements to theinitial value within a short time, whereby provided is a photoelectricconversion device with a high reliability.

The above-explained photoelectric converting element is provided, in theorder from the substrate side, with a first electrode layer, a firstinsulation layer for inhibiting the movement of both the carriers of afirst type and those of a second type different in polarity from thecarriers of the first type, a non-singlcrystalline photoelectricconverting semiconductor layer, a second electrode layer and aninjection inhibiting layer positioned between the second electrode layerand the photoelectric converting semiconductor layer and adapted toinhibit the injection of the carriers of the first type into thephotoelectric converting semiconductor layer.

Also there are provided a control unit, a power source unit and adetection unit for controlling the switch elements:

for applying an electric field to the above-mentioned layers of thephotoelectric converting element, in the refreshing mode, in such adirection as to guide the carriers of the first type from thephotoelectric converting semiconductor layer to the second electrodelayer;

for applying an electric field to the above-mentioned layers of thephotoelectric converting element, in the photoelectric conversion mode,in such a direction as to retain the carriers of the first type,generated by the light entering the photoelectric convertingsemiconductor layer, within the photoelectric converting semiconductorlayer and to guide the carriers of the second type to the secondelectrode layer; and

for detecting the carriers of the first type, accumulated in thephotoelectric converting semiconductor layer in the photoelectricconversion mode, or the carriers of the second type guided to the secondelectrode layer, as the light signals.

The above-mentioned switching element is provided, in the order from thesubstrate side, with a gate electrode layer, a second insulation layer,a non-singlcrystalline semiconductor layer, a main electrode layerconstituting a pair of first and second main electrodes separated by aportion of the above-mentioned semiconductor layer, constituting achannel area, and an ohmic contact layer positioned between the mainelectrode layer and the above-mentioned semiconductor layer.

At least a part of the photoelectric converting semiconductor layer andthe semiconductor layer mentioned above is composed of hydrogenatedamorphous silicon.

[Second embodiment]

This embodiment provides a photoelectric conversion device having anequivalent circuit diagram shown in FIG. 9 and capable of switching thedrive method with trimming according to the timing chart shown in FIG.10 and the drive method for reading all the pixels according to FIG. 6.

Such photoelectric conversion device is convenient for use, as thereading of all the pixels and the partial reading can be arbitrarilyselected according to the necessity.

For enabling such control, the present embodiment is provided, as in thefirst embodiment, with a control circuit A for controlling the shiftregisters SR1 and SR2. The partial reading and the reading of all thepixels can be switched by the entry, into the control circuit A, of thename of the required output signals in case of the trimmed reading, orof the name of the required output signals of all the pixels in case ofthe reading of all the pixels.

It is also possible to obtain high-definition moving image informationin the interest area while reading the peripheral area, by alternatelyeffecting or suitably switching the reading of all the pixels and thetrimmed reading.

The information obtained outside the trimmed area may not providesatisfactory moving image, but the satisfactory image reading can beachieved easily and securely in the necessary interest area.

[Third embodiment]

This embodiment provides, in the photoelectric conversion device shownin FIG. 9, another example of reading the output signals of thephotoelectric converting elements S21, S22 and S23 only. The drive untilthe charge accumulation by photoelectric conversion is same as in thefirst embodiment. Also the photoelectric conversion device can bebasically identical, in configuration with that of the first embodiment.

The accumulated charges are outputted in succession as signals v1-v3,through the transfer TFT's T21-T23 and the switches M1-M3, by theapplication of a Hi-level control pulse to the control line g2 and ofcontrol pulses to the control lines s1-s3 of the shift register SR2.Hi-level control pulses are not applied to the control lines g1, g3 fortransferring the unnecessary output signals of the photoelectricconverting elements S11-S13 and S31-S33.

These operations are illustrated in a timing chart in FIG. 11. In thiscase not all the control lines g1-g3 are driven after the exposure tothe X-ray irradiation, but the control line g2 alone, corresponding tothe desired reading area, is drive while other control lines g1, g3remain undriven.

As shown in FIG. 11, the control lines g1, g3 are also driven only at atiming when the control line g2 is also driven, for the purpose ofinitialization. In this manner the information of the interest area canalways be obtained with stable characteristics.

For enabling such control, the present embodiment is provided with acontrol circuit A for controlling the shift registers SR1 and SR2 asshown in FIG. 9. More specifically, the control circuit A generates asignal capable of starting the shift register SR1 from an arbitrarilydesignated address and stopping it at an arbitrarily designated address,and also generates start and stop signals for determining the addressesand the number of repetition of the register SR2 according to the numberof driven addresses of the register SR1. In this manner the outputsignals can be obtained from the required photoelectric convertingelements. Such control circuit, being capable of recognizing the enteredbit numbers of the sensors, is composed of logic circuits, but it mayalso be composed of circuits utilizing a microcomputer.

The required two-dimensional information, representing for example theinternal structure of the human body, can thus be obtained as v1-v3, bythe control of the shift registers SR1 and SR2 by the control circuit A.A still image can be obtained by the above-explained process, but suchprocess is repeated in order to obtain a moving image.

In the present embodiment there has been explained a case oftwo-dimensionally arranging nine pixels into a 3×3 matrix and outputtingthe signals of only three pixels therein, but the trimming can beachieved by driving, by the shift registers, any plural desired drivelines in succession.

In the present embodiment, in a photoelectric conversion device forreading in succession the signals from plural photoelectric convertingelements arranged in a two-dimensional array on a substrate, bysuccessively scanning the drive lines in the X-direction therebytransferring the signal charges in the signal lines in the Y-direction,the arbitrarily selected necessary drive lines alone are scanned insuccession while the remaining drive lines are not driven for thepurpose of signal charge transfer. Such photoelectric conversion device,capable of dispensing with the time required for driving the unnecessarydrive lines and for reading the unnecessary output signals, can read thenecessary signals at a higher speed. Thus, in case the photoelectricconversion device is utilized as an X-ray image capture device,particularly in case of observation of a moving image by continuousirradiation of such image capture device with X-ray, there can beachieved a reduction in the X-ray radiation dose, providing a medicallyand environmentally significant advantage, because the above-explaineddrive method practically corresponds to an increase in the sensitivity,as the exposure time can be extended if the number of exposures per unittime is maintained constant.

[Fourth embodiment]

This embodiment utilizes the photoelectric conversion device of thethird embodiment for switching the drive method with trimming accordingto the timing chart shown in FIG. 11 and the drive method for readingall the pixels according to FIG. 6.

This embodiment provides the convenience for use as in the secondembodiment, by switching the reading of all the pixels and the partialreading according to the necessity.

For enabling such control, the present embodiment is provided, as in thefirst embodiment, with a control circuit A for controlling the shiftregisters SR1 and SR2. The partial reading and the reading of all thepixels can be switched by the entry, into the control circuit A, of thename of the required output signals in case of the trimmed reading, orof the name of the required output signals of all the pixels in case ofthe reading of all the pixels.

Also in the present embodiment, an effect of moving image readingsimilar to that in the second embodiment can be obtained by alternatereading operations as in the second embodiment.

[Fifth embodiment]

Now reference is made to FIG. 12 for explaining a drive method for thephotoelectric conversion device, constituting the image signal readingmethod of the present embodiment, and an X-ray image capture systemutilizing the photoelectric conversion device enabling such drivemethod. However such system is naturally applicable also in theforegoing embodiments.

Referring to FIG. 12, an X-ray image capture system is composed of anX-ray chamber 101, an X-ray control room 102 and a diagnosis room 103.It is also possible to construct the X-ray image capture system withoutthe diagnosis room 103, and to connect a LAN as 103 to such X-ray imagecapture system.

The functions of the entire X-ray image capture system are controlled bya system control unit 110, which principally performs the followingfunctions. At first, it receives an instruction from an operator 105through a user interface 111, which can be, for example, a touch panelon a display, a mouse, a keyboard, a joy stick or a foot switch. Thecontent of such instruction may include the image capture conditions(still image, moving image, voltage and current of X-ray tube, X-rayirradiation time etc.), the image capture timing, the image processingconditions, the ID of the patient, the processing method for thecaptured image etc. Based on the image capture conditions instructedfrom the operator 105, the system control unit 110 sends an instructionto an image capture control unit 112, controlling the X-ray imagecapture sequence, and fetches the data. Based on the instruction fromthe system control unit 110, the image capture control unit 112 drivesan X-ray generating unit 120, an image capture base (specimen table) 130and an X-ray detector 140 to fetch image data, then transfers the imagedata to an image processing unit 150 for effecting the image processingdesignated by the operator, displays an image on a display 160 through adisplay drive circuit 151, and stores the basic image process data in anexternal memory 161. Then, also based on the instruction of the operator105, the system control unit 110 effects, for example, repeated imageprocessing, display of reproduced image, transfer of image data to thedevices on the network (LAN), storage of the image data, display thereofand/or printing thereof on a film.

In the following the system will be explained further, according to theflow of the signals.

The X-ray generating unit 120 is provided with an X-ray tube 121 and anX-ray diaphragm 123. The X-ray tube 121 is driven by a high-voltagesource 124 controlled by the image capture control unit 112 and emits anX-ray beam 125. The X-ray diaphragm 123, driven by the image capturecontrol unit 112, shapes the X-ray beam 125 for avoiding the X-rayirradiation to the unnecessary area, according to the change in theimage capture area. The X-ray beam 125 is directed to a specimen 126placed on the X-ray transmitting image capture table 130, which isdriven two-dimensionally, perpendicular to the irradiating direction ofthe X-ray beam 125, according to the instruction of the image capturecontrol unit 112. The X-ray beam 125 reaches the X-ray detector 140after passing the specimen 126 and the table 130.

The X-ray detector 140 is provided with a grid 141, a scintillator(fluorescent member) 142, a photoelectric converting element array(photodetector array) 143, an X-ray radiation dose monitor 144 and adrive circuit 145. The grid 141, serving to reduce the influence of theX-ray scattering caused by the transmission of the specimen 126, iscomposed of a low X-ray absorbing material and a high X-ray absorbingmaterial, such as Al and Pb arranged in a stripe structure. The grid 141is vibrated according to the instruction of the image capture controlunit 112, in order to avoid moire fringe generation by the relationshipof the grating structures of the photodetector array 143 and the grid141. In the scintillator 142, the base material of the fluorescentmember is excited by absorbing the X-ray of high energy and fluorescentlight of visible range by the energy of recombination. Such fluorescentlight is obtained either from the base material itself, such as CaWO₄ orCdWO₄, or from light emitting centers formed by activation materials inthe base material such as CsI:Tl or ZnS:Ag. Adjacent to the scintillator412 there is provided the photodetector array 143, which converts thephotons into electrical signals. The X-ray radiation dose monitor 144monitors the amount of the transmitted X-ray, either by directlydetecting the X-ray for example with a crystalline silicon photosensoror by detecting the light from the scintillator 142. As an example, thevisible light transmitted by the photodetector array 143 andproportional to the X-ray radiation dose may be detected by an amorphoussilicon photosensor formed on the substrate of the photodetector array143. The detection signal of the monitor 144 is supplied to the imagecapture control unit 112, which in response controls the high voltagesource 124 to intercept or regulate the X-ray. The drive circuit 145drives the photodetector array 143 and reads the signals from thedetecting elements, under the control of the image capture control unit112. The photodetector array 143 and the drive circuit 145 will beexplained later.

The image signal (image data) from the X-ray detecting unit 140 istransferred from the X-ray chamber 101 to the image processing unit 150in the X-ray control room 102. Since noises are often generated at theX-ray emission in the X-ray chamber 101, the transfer of the image datamay be affected by such noises. For this reason there is preferablyemployed a transmission path with a high noise resistance, such as atransmission system having error correcting function, shielded andtwisted paired wires combined with a differential driver, or an opticalfiber transmission path. The image processing unit 150 executes imagedata correction, spatial filtering, recursive process etc. on real-timebasis. It can also execute gradation process, correction for scattering,DR compression etc. The image thus processed is displayed on a displayunit 160. Simultaneously with the read-time image processing, the basicimage after data correction is stored in a high-speed memory 161, whichis preferably composed of a data storage device of a large capacity, ahigh speed and high reliability, for example a hand disk array such asRAID.

Also based on the instruction of the operator 105, the image data storedin the high-speed memory 161 are stored in an external memory device,with such data reconstruction as to satisfy a predetermined standard(such as IS&C). The external memory device is composed, for example, ofa magnetooptical disk 162 or a hard disk in a file server 170 on theLAN. The present X-ray image capture system can be connected to the LAN103 through a LAN board 163, and is to constructed as to be compatiblewith the data of the HIS (hospital information system). To the LAN,there may be connected not only plural X-ray image capture systems butalso a monitor 174 for displaying a still image or a moving image, afile server 170 for filing the image data, an image printer 172 forprinting the image on a film, an image processing terminal 173 foreffecting complex image processing and supporting the diagnosis etc. Thepresent X-ray image capture system releases the image data according toa predetermined protocol, such as DICOM. It also enables, by a monitorconnected to the LAN, the real-time remote diagnosis by the doctor atthe X-ray image capture.

FIG. 13 is a schematic plan view of a portion of four detecting elements(4 pixels) of an example of the photodetector array 143, and FIG. 14 isa cross-sectional view along a line 14--14.

Each detecting element is provided with a photoelectric convertingelement 401 and a switching element 402. In FIG. 13, a hatched areaindicates a light-receiving face of the photoelectric converting element401, for receiving the fluorescent light from the scintillator 141. Asignal charge, obtained by the photoelectric conversion in thephotoelectric converting element 401, is transferred to the processingcircuit through the switching element 402. There are also shown acontrol line 708 for controlling the switching element 402, a signalline 709 connected to the processing circuit, a power supply line 710for applying a bias to the photoelectric converting element, and acontact hole 720 connecting the photoelectric converting element 401 andthe switching element 402.

In the following there will be explained an example of the method forforming the detecting element including the photoelectric convertingelement and the switching element.

At first chromium (Cr) is evaporated by sputtering or by resistanceheating onto an insulating substrate 400 to form a first thin metal film721 with a thickness of about 500 Å. The film is then patterned by aphotolithographic process and the unnecessary areas are etched off. Thefirst metal film 721 constitutes the lower electrode of thephotoelectric converting element 401 and the gate electrode of theswitching element 402. Then a-SiNx (725), a-Si:H (726) and n⁺ -layer(727) are deposited in succession, by CVD in the same vacuumenvironment, with respective thicknesses of 2000, 5000 and 500 Å. Theselayers respectively constitute the insulation layer/photoelectricconverting semiconductor layer/hole injection inhibiting layer of thephotoelectric converting element 401, and the gate insulationlayer/semiconductor layer/ohmic contact layer of the switching element(TFT) 402. They are used also as an insulation layer in a crossing-area(730 in FIG. 13) of the first metal film 721 and a second metal film722. The thicknesses of these layers are not limited to theabove-mentioned figures but can be optimally designed according to thevoltage and charge of the detecting element, the amount of fluorescentlight entering from the scintillator etc. At least the a-SiNx layer 725preferably has a thicknesses of 500 Å or larger, in order to inhibit thepassing of the electrons and the holes and to satisfactorily function asthe gate insulation film of the TFT 402.

After the deposition of the above-mentioned layers, an area for formingthe contact hole (720 in FIG. 13) is dry etched by RIE or CDE, andaluminum (Al) is deposited, as a second metal film 722, by sputtering orby resistance heating, with a thickness of about 10,000 Å. The film isthen patterned by a photolithographic process and the unnecessary areasare etched off. The second metal film 722 constitutes the upperelectrode of the photoelectric converting element 401, the source anddrain electrodes of the switching TFT 402, and other wirings.Simultaneous with the formation of the second metal film 722, it isconnected with the first metal film 721 at the contact hole.

Also for forming the channel part of the TFT 402, an area between thesource and drain electrodes is etched by RIE, and then the unnecessarya-SiNx layer, a-Si:H layer and n⁺ -layer are etched off by RIE toisolate the elements. In this manner there are formed the photoelectricconverting element 401, the switching TFT 402, other wirings 708, 709,710 and the contact hole 720.

Though the cross-sectional view in FIG. 14 illustrates only two pixels,a plurality of the pixels are naturally formed simultaneously on theinsulating substrate 400. Finally, for improving the moistureresistance, the elements and the wirings are covered, for example, by apassivation film (protective film) 410 composed of SiNx (amorphousmaterial containing silicon atoms and nitrogen atoms).

As explained in the foregoing, the photoelectric converting element 401,the switching TFT 402 and the wirings can be formed by suitably etchingthe first metal film, the a-SiNx layer, the a-Si:H layer (amorphousmaterial based on silicon atoms and containing hydrogen atoms), the n⁺-layer (amorphous material based on silicon atoms and containinghydrogen atoms and phosphor or arsine atoms), and the second metal film,which are deposited in common and simultaneous manner. Also thephotoelectric converting element includes only one injection inhibitinglayer, which can be formed in the same vacuum chamber as that for otherlayers.

In the following there will be explained the function of thephotoelectric converting element 401 alone.

FIGS. 15A to 15C show the energy band of the photoelectric convertingelement 401, in a direction across the constituent layers thereof. FIGS.15A and 15B respectively show the function states in the refreshing modeand the photoelectric conversion mode, wherein shown are a lowerelectrode 721 composed of chromium (hereinafter written as G electrode),a SiNx insulation layer 725 for inhibiting the passing of the electronsand the holes, with a thickness of about 500 Å capable of inhibiting thepassing of the electrons and the holes even under the tunneling effect,a photoelectric converting semiconductor layer 726 which is an intrinsicsemiconductor layer composed of hydrogenated amorphous silicon a-Si:H,an injection inhibiting layer 727 which is an a-Si n-layer forinhibiting the injection of the holes into the photoelectric convertingsemiconductor layer 726, and an Al upper electrode 722 (hereinafterwritten as D electrode). Though the D electrode does not completelycover the n-layer, they are always at a same potential because of freeelectron movement therebetween, and this fact is utilized in thefollowing description. The photoelectric converting element has twofunction states, namely the refreshing mode and the photoelectricconversion mode, depending on the manner of voltage application to the Dand G electrodes.

In the refreshing mode, the D electrode is given a negative positionwith respect to the G electrode as shown in FIG. 15A, whereby the holesrepresented by the black circles in the i-layer 726 are guided by theelectric field to the D electrode. At the same time, the electronsrepresented by the white circles are injected into the i-layer 726. Inthis state, a part of the holes and a part of the electrons recombineand vanish in the n-layer 727 and in the i-layer 726. If this statecontinues sufficiently long, the holes in the i-layer 726 are removedtherefrom.

The refreshing mode is shifted to the photoelectric conversion mode bygiving a positive potential to the D electrode, with respect to the Gelectrode, as shown in FIG. 15B. In response, the electrons in thei-layer 726 are instantaneously guided to the D electrode. However theholes are not guided to the i-layer 726 since the n-layer 727 functionsas the injection inhibiting layer. If the light enters the i-layer 726in this state, the light is absorbed to generate pairs of electrons andholes. The electrons are guided by the electric field to the Delectrode. On the other hand, the holes move in the i-layer 726 andreach the interface with the insulation layer 725 and, as they cannotenter the insulation layer 725, they gather at the above-mentionedinterface. In response, a current flows out from the G electrode inorder to maintain the electrical neutrality of the element This current,corresponding to the electron-hole pairs generated by the light, isproportional to the amount of the incident light. If the element ismaintained in the photoelectric conversion mode shown in FIG. 15B for acertain period and is then shifted to the refreshing mode shown in FIG.15A, the holes retained in the i-layer 726 are guided to the D electrodeas explained above, and a current is simultaneously generatedcorresponding to these holes. The amount of such holes corresponds tothe total amount of the light received during the photoelectricconversion mode. In this state there is also generated a currentcorresponding to the amount of the electrons injected into the i-layer726, but the amount of such current, being almost constant, can besubtracted at the detection. In this manner the photoelectric convertingelement can output not only the amount of incident light on real-timebasis but also the total amount of light received in a certain period.

However, if the period of the photoelectric conversion mode is extendedor the intensity of the incident light becomes stronger for some reason,the current generation may be suspended despite of the presence of theincident light. Such situation is induced by a fact that a large numberof holes remain in the i-layer 726 and recombine with the generatedelectrons. There may be generated an unstable current if the state ofthe incident light varies in this state, but the holes in the i-layer726 are removed by shifting the element to the refreshing mode again,and a current proportional to the incident light is obtained again inthe next photoelectric conversion mode.

In removing the holes from the i-layer 726 in the refreshing modeexplained above, it is desirable to remove all the holes, but a partialremoval of the holes is also effective and can provide a current same asexplained above. More specifically it is required that the state shownin FIG. 15C does not occur at the detection in the next photoelectricconversion mode, and the potential of the D electrode relative to thatof the G electrode in the refreshing mode, the period thereof and thecharacteristics of the injection inhibiting n-layer 727 can be soselected as to satisfy such requirement. Also in the refreshing mode,the electron injection into the i-layer 726 is not essential. Also thepotential of the D electrode need not necessarily be negative relativeto that of the G electrode, since, in case a large number of holesremain in the i-layer 726, the electric field therein is generated in adirection to guide the holes toward the D electrode even if thepotential of the D electrode is positive relative to that of the Gelectrode. Also the injection inhibiting n-layer 727 is not necessarilyrequired to inject the electrons into the i-layer 726. The foregoingexplanation of the photoelectric converting element is basicallyapplicable to the foregoing embodiments.

In the following there will be explained the function of the detectingelement of a pixel in the X-ray image capture device, with reference toFIGS. 16 and 17.

FIG. 16 is an equivalent circuit of a pixel, including the photoelectricconverting element 401 and the switching TFT 402, and FIG. 17 is atiming chart showing the function of such circuit. As explained in theforegoing, the present detecting element has two modes, namely therefreshing mode for initializing the photoelectric converting element401, and the photoelectric conversion mode for accumulating the receivedlight in the form of a charge.

Immediately after the power supply is turned on, there is assumed therefreshing mode in order to initialize the photoelectric convertingelement 401. A bias power source 701 applies a voltage corresponding tothe mode (refreshing mode or photoelectric conversion mode). In therefreshing mode, the bias power source 701 is set at a voltage Vr forthe refreshing mode, and a voltage Vgh is applied to the gate 730 of theswitching TFT 402 to turn on the TFT 402. At the same time, a resettingswitch element 705 is turned on, whereby the D and G electrodes of thephotoelectric converting element 401 are respectively set at a voltageVr and a bias voltage VBT of a resetting power source 707 (Vr<VBT).

After the lapse of a predetermined time, the circuit is shifted from therefreshing mode to the photoelectric conversion mode, in which the biaspower source 701 is set at a voltage Vs for the photoelectric conversionmode and the switching TFT 402 is turned off. At the same time theresetting switch element 705 is turned off, and the charge accumulationin capacitors C1 and C2 is started immediately thereafter.

Immediately after the shift from the refreshing mode to thephotoelectric conversion mode, the photoelectric conversion unit has alarge dark current. In order to suppress the influence of such darkcurrent, the G electrode in the photoelectric converting element 401 isagain set at a voltage VBT after the lapse of a predetermined time fromthe shift to the photoelectric conversion mode. In more details, whilethe bias power source 701 is maintained at a voltage Vs, the resettingswitch element 705 is turned on to maintain a capacitance element 713 ata voltage VBT, and the resetting switch element 705 is then turned off.Then the switching TFT 402 is turned on while the bias power source 701is maintained at the voltage Vs, thereby resetting the capacitor C1 inthe photoelectric converting element 401. The accumulation of the signalcharge in the capacitor C1 of the photoelectric converting element 401is initiated when the switching TFT 402 is turned off.

Subsequently the X-ray generating unit 120 emits the X-ray 125, which isconverted, after passing the specimen 126 and the grid 141, by thescintillator 142 into the light in the sensitivity range (for examplewavelength λ=550 nm) of the photoelectric converting element 401, andthus converted light is further subjected to the photoelectricconversion in the photoelectric converting element 401. As the a-SiNxinsulation layer 725 and the a-Si:H photoelectric semiconductor layer726, constituting the photoelectric converting element 401, aredielectric, the element 401 functions as a capacitance element andstores the signal charge in the capacitor C1 therein.

After the X-ray irradiation, the TFT 402 is turned on to transfer theaccumulated charge signal from the capacitor C1 in the element 401 to acapacitance element 713. In fact electrons flow from the capacitanceelement 713 into the capacitor C1. The capacitance element 713 is notparticularly formed as an element in the circuit shown in FIG. 13, butis inevitably formed by the capacitance between the upper and lowerelectrodes of the TFT 402 or by a crossing portion 730 of the signalline 709 and the gate line 708. However it may naturally be designed andprepared as a separate element.

The above-explained operations, except for the power supply and thecontrol of the TFT 402, are executed by amorphous devices formed on theinsulating substrate.

Then the signal potential of the capacitance element 713 is amplified 10to 100 times by a pre-amplifier 721, and is held in a succeedingsample-hold unit 750 at a timing shown in FIG. 17. The amplificationgain is fixed during the measurement, but is switchable by aninstruction from a system control unit 110, according to the purpose ofthe operator. The pre-amplifier 721 and the sample-hold unit 750 may bereplaced by a current-voltage converting circuit. While the sample-holdunit 750 releases the signal to the subsequent circuits, thephotoelectric converting element 401 effects at the same time theaccumulation of the signal charge and the charge transfer to thecapacitance element 713, and the driving speed per element is elevatedby such pipeline process. The output of the sample-hold unit 750 issupplied through an analog multiplexer 751 (of which drive method willbe explained later in the description of two-dimensional drive) to threeamplifiers 752 (752-1, 752-2, 752-3), having respective gains of x1, x2and x4 and respectively connected to A/D converters 760-1, 760-2, 760-3.The A/D converters 760 complete the A/D conversion while the signal ofthe analog multiplexer 751 is fixed, then select an effective A/Dconversion output from the converters 760-1, 760-2, 760-3 based on anoverflow signal of the input signal to the A/D converters 760, andprovides the succeeding image process unit 150 with the selected A/Dconversion output together with the overflow signal of the A/Dconverters 760. By the above-explained configuration, the three A/Dconverters function as a single A/D converter with automatic rangeswitching function.

Then, in order to again read the signal charge (accumulated after theTFT gate 730 is turned off before) from the capacitor C1 of thephotoelectric converting element 401, a resetting switch element 705 isturned on while the gate 730 is turned off, thereby resetting thecapacitance element 713 to the voltage VBT. After this state is reached,the resetting switch element 705 is turned off, and the gate 730 of theTFT 402 is turned off. Thus a signal charge, corresponding to the amountof X-ray irradiation from the previous turn-off of the TFT 402 to thepresent turn-on thereof, is sent to the capacitance element 713.Thereafter the signals can be read in succession, by repetition of theabove-explained signal reading operation from the capacitance element713.

As the capacitor C2 in the photoelectric converting element 401 becomessaturated by the continuation of the signal reading operation, it isnecessary to shift the element from the photoelectric conversion mode tothe refreshing mode at a predetermined interval and to refresh theelement by removing the charge (positive holes) accumulated in thecapacitor C2 of the photoelectric converting element 401. The signalreading is executed by repeating the above-explained operations.

For obtaining the charge signal of a higher S/N ratio, there may beexecuted a correction for the offset error resulting from the darkcurrent. As the dark current of the above-explained photoelectricconverting element is known to exponentially decrease as a function oftime, a signal reading operation is repeated without X-ray irradiationat a predetermined time after the above-explained signal readingoperation. The signal obtained by such repeated signal readingcorresponding to the offset caused by the dark current, and thecorrection for the offset by the dark current can be made for thepreviously obtained signal including the X-ray irradiation, based onsuch offset value, the charge accumulation time and the time after therefreshing. In case of capturing a still image, the data correction canbe made by a software process after the image data are fetched forexample in a RAM in the image process unit 150. In case of a movingimage, the offset correction may be achieved by repeating the reading ofthe X-ray irradiation signal and that of the dark current in everypredetermined accumulation time, storing thus read signals for examplein a RAM and effecting digital subtraction by a hardware process.

In the following there will be explained a photoelectric convertingoperation in case the detecting element shown in FIG. 16 is expanded toa two-dimensional array. FIG. 18 is an equivalent circuit diagram of atwo-dimensional array of the photoelectric converting elements, and FIG.19 is a timing chart showing the function thereof.

A photodetector array 143 is composed of 2000×2000 to 5000×5000detecting elements (pixels) and has an area of 200×200 to 500×500 mm. InFIG. 17, the array 143 is composed of 4096×4096 pixels of an area of430×430 mm, so that each pixel has a size of 105 μm. A two-dimensionalarray is obtained by arranging 4096 pixels of a block in a horizontalline, and arranging such 4096 lines in the vertical direction.

In the above-explained configuration, the photodetector array of4096×4096 pixels is formed on a single substrate, but it may also becomposed of four photodetector arrays each having 2048×2048 pixels. Suchdivided configuration provides the advantage of an improved yield in themanufacture.

As explained in the foregoing, each pixel is composed of a photoelectricconverting element 401 and a switch TFT 402. The array has photoelectricconverting elements 401-(1, 1) to 401-(4096, 4096), in which G and Drespectively indicate the lower and upper electrodes, and switching TFT402-(1, 1) to 402-(4096, 4096). The G electrodes of the photoelectricconverting elements 401-(m, n) in each column of the two-dimensionalphotodetector array are connected, by the source-drain conductive pathsof the corresponding switching TFT's 402-(m, n), to a common columnsignal line (Lc 1 to 4096) for that column. For example thephotoelectric converting elements 401-(1, 1) to 401-(4096, 4096) of thefirst column are connected to the first column signal line Lc1.

The D electrodes of the photoelectric converting elements 401 of eachrow are commonly connected, through a bias line Lb, to the bias powersource 701 for controlling the aforementioned modes. Also the gateelectrodes of the TFT 402 of each row are connected to a row selectingline (Lr 1-4096). For example the TFT 402-(1, 1) to 402-(4096, 1) of thefirst row are connected to the row selecting line Lr1. The row selectinglines Lr are connected to a line selector unit 810, composed of anaddress decoder 811 and 4096 switch elements 812 and serving to read anarbitrary line Lrn. In simplest manner, the line selector 810 can alsobe composed of a shift register.

The column signal lines Lc are connected to a signal reading unit 820controlled by the image capture control unit 112. The signal readingunit 820 is same, for each pixel, as the configuration already explainedin FIG. 16.

In this image capture device, the 4096×4096 pixels are divided into 4096lines (corresponding to Lr or the horizontal row in FIG. 18), and theoutputs of 4096 pixels of a row are simultaneously transferred throughthe column signal lines Lc, the pre-amplifiers 721-1 to 721-4096 and thesample-hold units 750-1 to 750-4096, and are then released by an analogmultiplexer 751 in succession to the A/D converter 760. In FIG. 18,there is illustrated only one A/D converter 760, but the A/D conversionmay also be executed simultaneously in 4 to 32 lines, and suchconfiguration allows to reduce the image signal reading time withoutunnecessarily increasing the analog signal band or the A/D conversionrate. The charge accumulation time is closely related to the A/Dconversion time, and the time required for the A/D conversion of all thepixels is always longer than the charge accumulation time, because aproper image cannot be obtained if the X-ray irradiation is conductedduring the charge transfer operation. A longer charge accumulation timeresults in an increase in the noise in the accumulated charge because ofthe dark current. On the other hand, in case of a high-speed A/Dconversion, it is difficult to attain a desired S/N ratio because of theexpanded bandwidth of the analog circuits. It is therefore required toreduce the reading time for the image signal without excessivelyincreasing the A/D conversion speed. For this purpose the A/D conversionmay be conducted with plural A/D converters 760, but an increased numberof the A/D converters results in a higher cost. A suitable number of theA/D converters is to be selected in consideration of these factors.

Since the X-ray irradiation time is about 10 to 500 msec., the imagefetching time or the charge accumulation time is preferably selected asabout 100 msec. or somewhat shorter. If the analog signal bandwidth isselected as about 50 MHz and the A/D conversion is executed for examplewith a sampling rate of 10 MHz, the image fetching at 100 msec. requiresat least 4 systems of the A/D converters 760. In the present imagefetching device, the A/D conversion is preferably executed in 16 systemsat the same time.

Referring to FIG. 19, immediately after the power supply is turned on orbefore the capacitor C2 in the photoelectric converting element 401 issaturated with the accumulated charge, the refreshing mode is assumed inorder to initialize the photoelectric converting element 401. As alreadyexplained with respect to the photoelectric converting element of eachpixel, the image capture control unit 112 shifts a bias line Lb to abias Vr for the refreshing mode and turns on the transfer switchingTFT's 402-(1, 1) to 402-(4096, 1) of the first row and the resettingswitch element 705 to refresh the G electrodes of the photoelectricconverting elements 401-(1, 1) to 401-(4096, 1) of the first row to VBTand the D electrodes thereof to Vr. Then the image capture control unit112 shifts the bias line Lb to a bias Vs for the photoelectricconversion mode and cuts off the column signal lines Lc1-Lc4096 of thefirst to 4096th columns from the resetting power source 707, and turnsoff the transfer switching TFT's 402-(1, 1) to 402-(4096, 1).Subsequently the photoelectric converting elements 401 of the second andsubsequent rows are refreshed in a similar manner. When the refreshingis executed to the 4096th row, the refreshing mode expanded to thetwo-dimensional photodetector array is completed and the operation isshifted to the photoelectric conversion mode. In the foregoingexplanation, the refreshing of the photoelectric converting elements 401is conducted from the first row to the 4096th row, but it may beexecuted in an arbitrary order by the instruction of the image capturecontrol unit 112. It is also possible to simultaneously turn on all theTFT's 402, thereby refreshing all the photoelectric converting elements401-(1, 1) to 401-(4096, 4096).

As the photodetector element 402 has a large noise charge immediatelyafter the refreshing operation, it is reset to the reference potential.As already explained with respect to the photoelectric convertingelement of each pixel, the bias line is maintained at the bias Vs forthe photoelectric conversion mode, and the transfer switching TFT's402-(1, 1) to 402-(1, 4096) are turned on to reset the G electrodes ofthe photoelectric converting elements of the first column to VBT. Thenthese TFT's are turned off. Subsequently, all the pixels are reset byrepeating the above-explained operation starting from the second column.For the amorphous element 800, this operation is same as the signalcharge reading operation except for a difference whether or not to fetchthe signal charge and to effect the A/D conversion. Such resettingoperation, selecting each TFT 402 but not executing the A/D conversion,will hereinafter be called "dummy reading". In such dummy readingoperation, though it is possible to simultaneously turn on all the TFT's402-(1, 1) to 402-(4096, 4096), the potential of the signal lines insuch case becomes significantly shifted from the reset voltage VBT atthe completion of preparation for the reading operation, so that thesignals of a high S/N ratio are difficult to obtain. In the foregoingexample, the row selecting lines Lr are reset from the first to 4096thbut the resetting may be executed in an arbitrary order under theinstruction from the image capture control unit 112. As the chargeaccumulation starts when the TFT 402 is turned off in each photoelectricconverting element 401, the every element 401 has different chargeaccumulation starting time.

In FIG. 19, a pulse train 730' conceptually indicates that a pulse turnson the TFT's of a column. The output of the analog multiplexer 751,indicated at a point B in FIG. 18, corresponding to a pulse in suchpulse train, is schematically shown by B in FIG. 19. As shown therein,the analog output corresponding to a pulse in the pulse train is givenby a pulse train consisting of 4096 pulses. More precisely, since theoutput signals of a column are given through 16 channels, 16 pulsesignals are released simultaneously and the A/D conversion is executedfor a pulse train consisting of 256 pulses.

After the dummy reading of all the photoelectric converting elements 401is completed, such dummy reading operation is repeated at apredetermined interval and the refreshing operation is also repeated ata longer interval, until an instruction for starting the image captureis given by the operator 105. Upon receiving such instruction, the imagecapture control unit 112 waits until the completion of the dummy readingoperation and effects the irradiation of the specimen 126 with X-ray.The X-ray beam 125 transmitted by the specimen 126 is converted by thescintillator 142 into a visible light, which is absorbed by thephotoelectric converting elements 401. At the same time, the visiblelight transmitted by the photodetector array 143 is detected by themonitor 144. Based on the detection signal thereof, the image capturecontrol unit 112 terminates the X-ray irradiation when an appropriateX-ray radiation dose is reached.

After the X-ray irradiation, the signal charges are read from thephotoelectric converting elements 401. At first, as in the dummy readingoperation, the TFT's of a row in the photodetector array (for example402-(1, 1) to 402-(4096, 1)) are turned on to release the accumulatedsignal charges to the signal lines Lc1 to Lc4096, from which the signalsof 4096 pixels are simultaneously read. After the signal lines Lc arereset, the TFT's 402 of a different row (for example 402-(1, 2) to402-(4096, 2)) are turned on to release the accumulated signal chargesto the signal lines Lc1 to Lc4096, from which the signals of 4096 pixelsare simultaneously read. This operation is repeated in succession forall the rows thereby obtaining the entire image information.

After the reading of the signal charges obtained by the X-rayirradiation, the signal charges without the X-ray irradiation are alsoread, in order to correct the influence of the dark current etc. in suchsignal charges based on the X-ray irradiation. The image signals at theX-ray irradiation can be corrected in the following manner, by thosewithout the X-ray irradiation.

In the above-explained operation, the charge accumulation period foreach sensor is from the completion of the resetting operation, namelyfrom the turn-off of the TFT 402 at the dummy reading, to the nextturn-on of the TFT 402 for the charge reading operation. Thus the periodand time of accumulation are different for each row selecting line Lr.As the correction becomes complex for such different accumulatingperiods, the image capture control unit 112 ordinarily drives thephotodetector array 143 in such a manner that the accumulation time issame for the image based on the X-ray irradiation and for the correctingimage. For example, the control is executed in such a manner that theaccumulation period Ti of the first row becomes equal to that T2 of the4096th row, though they occur at different times.

In case the image information of a high resolution is not required or incase a higher rate of image data fetching is desired, it is not alwaysnecessary to fetch all the image information, and the image capturecontrol unit 112 may execute image skipping, pixel averaging or areaextraction according to the selection of the operator.

The image skipping can be achieved by at first selecting the rowselecting line Lr1, and, at the output of the signals of a row from thecolumn signal lines Lc, by selecting every other column signal linesLc(2n-1) starting from n=1, wherein n is a natural number. Also in theselection of rows, the signals are read from every other row byselecting the row selecting lines Lr(2m+1) starting from m=1, wherein mis a natural number. In this example, the number of pixels is skipped to1/4, but the skipping can also be realized for example at 1/9 or 1/16according to the instruction from the image capture control unit 112.

The pixel averaging can be realized, in the above-explained operation,by applying Vgh simultaneously to the row selecting lines Lr(2m-1) andLr(2m) to simultaneously turn on the TFT 402-(2n, 2m-1) and the TFT402-(2n, 2m) thereby achieving analog addition of the two pixels in thedirection of column. Such addition is not limited to two pixels, but ananalog addition of three or more pixels arranged along the column signalline Lr can be easily achieved. Also the addition in the direction ofrow can be achieved by a digital addition of the signals of mutuallyadjacent columns (Lc(2n) and Lc(2n+1)) after the A/D conversion. Thus,in combination with the analog addition mentioned above, there can beobtained the added value of 2×2 pixels in a matrix arrangement. In thismanner the data can be read at a high speed, without wasting theirradiating X-ray. It is naturally possible also to effect averaging ina matrix other than 2×2, and high-speed image capture with a matrix forexample 3×3 or 4×4 can be achieved according to the instruction of theimage capture control unit 112.

The area extraction is to achieve a higher speed by reducing the numberof pixels to be read, and is realized by limiting the image readingarea. The operator 105 instructs a necessary area through the operatorinterface 111, and, based on such instruction, the image capture controlunit 112 varies the data reading area in driving the two-dimensionaldetector array 143.

As an example of such drive, let us consider a case of capturing, in ahigh-speed image capture mode, the data of 1024×1024 pixels at a rate of30 frames/sec. In such case, if the image is captured over the entirearea of the two-dimensional detector array 143, the number of pixels isskipped to 1/16 by an addition process of 4×4 pixels, but, if the imageis captured in a smallest area, the image is captured without skippingin an area of 1024×1024 pixels. Such operation enables digital zoomingof the image.

In the following there will be explained the interest area. At firstthere will be explained the method for setting the image capture area inthe present X-ray image capture device, with reference to FIG. 20.

In FIG. 20, there are shown a moving image display 901, a display drivecircuit 902 therefor, a still image display 905 and a display drivecircuit 906 therefor.

An interface 111 to be used by the operator for instructing the imagecapture area and the X-ray irradiation is provided, for example, with animage capture position controlling lever 911, an image capture sizeselecting switch 912, an image capture zoom/wide lever 913, a manualX-ray diaphragm lever 914, a radioscopy start switch 915, a radioscopyimage enlarging switch 916, and a high-definition image capture switch917.

The image capture position controlling lever 911 moves the centerposition of the image capture area. If the instruction by this lever 911is within the range of the photodetector array 143, the system controlunit 110 does not move the specimen table 130 but moves the X-raydiaphragm 123 only, thereby varying the position of the X-rayirradiation. If the instruction is outside the range of thephotodetector array 143 but within a range that can be covered by themovement of the specimen table 130, the system control unit 110 movesthe specimen table 130. At the same time the X-ray diaphragm 123 is alsomoved so as to match the center of the photodetector array 143 with thatof the X-ray irradiation.

The image capture size selecting switch 912 is to select the size of theimage capture size, for example from the following three sizes of imagecapture.

    ______________________________________                                        Vertical × Horizontal                                                   ______________________________________                                        1. 1 × 1   (43 × 43 cm)                                           2. 3/4 × 3/4                                                                             (32 × 32 cm)                                           3. 1/2 × 1/2                                                                             (21 × 21 cm)                                           ______________________________________                                    

When the operator 105 selects one of these sizes, the system controlunit 110 at first moves the specimen table 130 to match the center ofthe photodetector array 143 with that of the X-ray irradiation, and thendrives the X-ray diaphragm 123 to adjust the X-ray irradiation area tothe selected image capture size. At the same time the system controlunit 110 instructs the drive circuit 145 for the photodetector array 143to fetch the image of the selected area.

The image capture wide/zoom lever 913 allows to vary the image capturearea almost arbitrarily, according to the operation of the operator 105.The image capture area selected by the image capture size selectingswitch 912 mentioned above is temporary and can be arbitrarily set bythis image capture zoom/wide lever 913. In the variation of the imagecapture area, if the area overflows the area selectable by the imagecapture size selecting switch 912, the spatial resolution on thephotodetector array 143 at the transmission observation is variedautomatically in such overflowing portion. More specifically, theautomatic variation of the resolution takes place in the followingmanner:

    ______________________________________                                        Vertical × Horizontal  Resolution                                       ______________________________________                                        1. 1 × 1  (43 × 43 cm) or less                                                                 1/4                                              2. 3/4 × 3/4                                                                            (32 × 32 cm) or less                                                                 1/3                                              3. 1/2 × 1/2                                                                            (21 × 21 cm) or less                                                                 1/2                                              ______________________________________                                    

Such variation can be achieved by a change in the drive method of thedrive circuit 145, so as to effect addition and averaging of 4×4 pixelsfor a resolution of 1/4, 3×3 pixels for a resolution of 1/3 and 2×2pixels for a resolution of 1/2. Naturally the averaging of a largernumber of pixels reduces the resolution but increases the sensitivityper displayed pixel.

The manual X-ray diaphragm lever 914 is used by the operator 105 foravoiding the X-ray irradiation to unnecessary areas outside the areaselected by the image capture zoom/wide lever 913 or for avoiding entryof a strong X-ray, such as flare, into the photodetector array. Themanual X-ray diaphragm lever 914 allows the operator 105 to directlymanipulate the X-ray diaphragm 123. However, the adjustable range of theX-ray diaphragm 123 is limited by the system control unit 110 in such amanner that the irradiation does not take place over an area wider thanthat selected by the image capture size selecting switch 912 or by theimage capture zoom/wide lever 913.

The radioscopy start switch 915 can be composed of a foot switch, to beused by the operator 105 for instructing the X-ray irradiation forradioscopy. When the start of radioscopy is instructed by the startswitch 915, the image capture control unit 112 executes the radioscopyby automatically regulating the X-ray generating condition, based on theoutput from the X-ray radiation dose monitor 144.

The radioscopy image enlarging switch 916 is actuated, if the resolutionin the central portion of the image capture area is to be elevated inthe course of radioscopic observation, to display an enlarged image ofthe central portion, with an improved resolution. At the radioscopicobservation, the spatial resolution is reduced in order to achievehigh-speed image capture, but, when the radioscopy image enlargingswitch 916 is selected, the system control unit 110 reduces the imagecapture area while maintaining the spatial resolution in an optimumstate, thereby displaying an enlarged image on the moving image display901. At the same time the X-ray diaphragm 123 is set at a size matchingthe image capture area. When the selection is terminated, the imagecapture area and the X-ray diaphragm 123 return to the original settingto continue the radioscopic observation.

The high-definition image capture switch 917 is selected in case ofcapturing a high-definition image at a desired timing in the course ofradioscopic observation. This switch is normally provided on the imagecapture position controlling lever 911. When the capture of a stillimage is instructed by the switch 917, the X-ray is emitted to thespecimen 126 under a predetermined X-ray generating condition for astill image, and a high-definition still image is fetched, processed inthe image process unit 150 and displayed on the still image display 905.During the capture of the still image, the moving image display 901continues to display the radioscopic image immediately before theactuation of the high-definition image capture switch 917.

The image capture area is determined by the configuration explained inthe foregoing. The interest area, determined by a desired range of rowsand a desired range of columns, is most simply defined as same to theimage capture area. In such case, the interest area is determined by theimage capture size selecting switch 192 or the image capture zoom/widelever 913. The image capture in the image capture area is executed,based on the center coordinate of the photodetector array 143 and thecoordinates of the image capture area, recognized by the system controlunit 110. The X-ray irradiation area may also be defined as the interestarea. In this case, the X-ray irradiation area and the center coordinatethereof can be determined by simple calculations, since the position ofthe X-ray diaphragm 123 is recognized by the system control unit 110.The system control unit 110 controls the drive circuit 145 to executethe image capture, based on such coordinate. An example of sequence forthe image capture will be explained later. There may be adopted otherconfigurations in which the operator 105 directly designates the centerof the interest area on the moving image display 901 with a pointer suchas a mouse, or which extracts the features of an area marked by theoperator 105 and automatically controls the X-ray diaphragm 123 and thespecimen table 130 in such a manner that the marked portion always comesto the center of the radioscopic image, thus driving the drive circuit145 maintaining the center of the interest area always at the center ofthe image capture area.

Now reference is made to FIG. 21 for explaining an example of the actualimage capturing sequence.

On the photodetector array 143, the X and Y axes are respectively takenin the directions of the row selecting line Lr and the column signalline Lc, and the coordinate of the pixel is represented by (x, y). InFIG. 21, it is assumed that the signal reading unit 820 including theA/D converter 760 etc. is positioned in the upper part of thephotodetector array 143 while the line selector unit 810 is provided inthe right-hand part, and the X-ray irradiates from the rear side of thedrawing toward the front side. The pixels are numbered as (1, 1) at theupper right corner and (4096, 4096) at the lower left corner.

It is also assumed that the center of the image capture area 200 ispositioned at (1750, 2250) by the image capture position controllinglever 911, that the image capture area 200 is set in a range of (500,1000) to (3000, 3500) by the image capture zoom/wide lever 913, and thatthe X-ray irradiation area 210 is set in a range of (500, 2000) to(3000, 3500) by the manual X-ray diaphragm lever 914. It is also definedthat the interest area of the operator 105 coincides with the X-rayirradiation area 210. Under such conditions, the center of the interestarea is at (1750, 2250) while the interest area is smaller than 3/4×3/4but larger than 1/2×1/2 of the area of 4096×4096 pixels, so thataddition averaging of 3×3 pixels is executed at the radioscopicobservation as explained in the foregoing. Consequently the rows to beread in FIG. 21 at the radioscopic observation are read in the followingmanner. In the following there is also written an example of radioscopicimage capture in case the selected area covers (m+1)-th line to (m+n)-thlines along the Y-axis, wherein n is a multiple of 6.

[Reading order]

The reading order (A), the selected rows (in case of 2001st-3500th rows)(B) and the selected rows (in case of (m+1)th-(m+n)th rows) arecorrelated as follows:

    ______________________________________                                                 Selected rows                                                        Reading  (2001st-3500th                                                                            Selected rows                                            order    rows)       ((m + 1)th-(m + n)th rows)                               ______________________________________                                        1        2001,2002,2003                                                                            m + 1,m + 2,m + 3                                        2        3500,3499,3498                                                                            m + n,m + n - 1,m + n - 2                                3        2004,2005,2006                                                                            m + 4,m + 5,m + 6                                        4        3497,3496,3495                                                                            m + n - 3,m + n - 4,m + n - 5                            5        2007,2008,2009                                                                            m + 7,m + 8,m + 9                                        6        3494,3493,3492,                                                                           m + n - 6,m + n - 7,m + n - 8                            .        .                .                                                   .        .                .                                                   .        .                .                                                   499 = (n/3 - 1)                                                                        2748,2749,2750                                                                            m + n/2 - 2,m + n/2 - 1,m + n/2                          500 = (n/3)                                                                            2753,2752,2751                                                                            m + n/2 + 3,m + n/2 + 2,m + n/2 + 1                      501 = (n/3 + 1)                                                                        2001,2002,2003                                                                            m + 1,m + 2,m + 3                                        502 = (n/3 + 2)                                                                        3500,3499,3498                                                                            m + n,m + n - 1,m + n - 2                                .        .                .                                                   .        .                .                                                   .        .                .                                                   ______________________________________                                    

(Hereafter correlation repeats in the same manner.)

If the capture of a high-definition image is instructed by thehigh-definition image capture switch 917 in the course of a radioscopicobservation, the capture of the radioscopic image is interrupted and theimage on the moving image display 901 is frozen, and the sequence shiftsto a drive routine for the X-ray irradiation area 210 forhigh-definition image capture. At first the photodetector array 143 isshifted to the refreshing mode and is refreshed. Then the photodetectorarray 143 is initialized in a driving direction from the periphery ofthe X-ray irradiation area 210 toward the center thereof, correspondingto the dummy reading operation explained in the foregoing, asexemplified in the following:

    ______________________________________                                        Reading  Selected rows  Selected rows                                         order    (2001st-3500th rows)                                                                         ((m + 1)th-(m + n)th rows)                            ______________________________________                                        1        2001           m + 1                                                 2        3500           m + n                                                 3        2002           m + 2                                                 4        3499           m + n - 1                                             5        2003           m + 3                                                 6        3498           m + n - 2                                             . . .    . . .          . . .                                                 1499 = (n - 1)                                                                         2750           m + n/2                                               1500 = n 2751           m + n/2 + 1                                           ______________________________________                                    

After the dummy reading operation is repeated plural (two to three)times, the X-ray irradiation is executed with the condition for stillimage capture. After the X-ray irradiation, the image signals are readin a driving order from the center of the X-ray irradiation area 210toward the periphery thereof, as exemplified in the following:

    ______________________________________                                        Reading  Selected rows  Selected rows                                         order    (2001st-3500th rows)                                                                         ((m + 1)th-(m + n)th rows)                            ______________________________________                                        1        2750           m + n/2                                               2        2751           m + n/2 + 1                                           3        2749           m + n/2 - 1                                           4        2752           m + n/2 + 2                                           5        2748           m + n/2 - 2                                           6        2753           m + n/2 + 3                                           . . .    . . .          . . .                                                 1499 = (n - 1)                                                                         2001           m + 1                                                 1500 = n 3500           m + n                                                 ______________________________________                                    

After such reading operation, the array is immediately shifted to theradioscopic image capture mode.

The above-explained reading drive allows to minimize the signal chargeaccumulation time for the high-definition image in the central portionof the interest area, thereby suppressing the influence of noisesresulting from the dark current.

The area outside the interest area of the present embodiment may be readcollectively at the same time or be initialized without signal reading,as already explained in the first and third embodiments.

The collective reading may be executed, not only simultaneously over theentire non-image-reading area, but also by dividing such area into acertain number of portions. Otherwise, after the signals are read fromthe image-reading area, the collective reading may be executed over allthe pixels including those already read.

As explained in the foregoing, the present invention enables high-speedsignal reading even in a photoelectric conversion device having atwo-dimensional array of plural photoelectric converting elements.

Also the present invention allows to dispense with the time forsuccessively driving unnecessary drive lines and the time for readingunnecessary output signals, thereby enabling to read the signals of anecessary portion at a high speed.

Also the present invention allows to equalize the sensor characteristicsof all the photoelectric converting elements, by simultaneouslyreturning the potentials at both ends of the unnecessary photoelectricconverting elements to initial values within a short time, therebyproviding photoelectrically converted information with higherreliability.

Also the present invention allows to switch a driving method with imagetrimming and a driving method for reading all the pixels, therebyproviding a photoelectric conversion device which can select the readingwith all the pixels or the reading with a part of the pixels and isconvenient for use.

Furthermore, the present invention allows, in driving an image capturedevice utilizing a photodetector array, to at first set an interest areaand to appropriately select the drive of the photodetector array withrespect to such interest area.

Also the present invention allows, particularly in readinghigh-definition image data, to reset the photoelectric convertingelements in succession from the periphery of the interest toward thecenter thereof, thereby selecting the signal charge accumulation time atthe central portion shorter than that at the periphery, thus suppressingthe influence of noises which increase together with the chargeaccumulation time and improving the S/N ratio in the central portion ofthe interest area.

Furthermore, the present invention allows, in case the photoelectricconversion device is utilized as an X-ray image capture device,particularly in case of a moving image observation by continuous X-rayirradiation on the X-ray image capture device, to reduce the X-rayradiation dose, thereby reducing the influence of radiation, such asX-ray, to the irradiated specimen, the operator of the device and theenvironment.

Though the foregoing embodiments have been directed to the X-ray imagecapture, the present invention is not limited to such application but islikewise applicable to any system employing an XY-addressablephotodetector array. The present invention is particularly effective inimproving the photoelectric converting characteristics, when it isapplied to a system employing a photodetector array, in which thephotoelectric converting element constituting a light-receiving unitincludes a signal charge accumulating unit and a switch unit positionedin a signal reading path and has a tendency to show deterioration in thephotoelectric converting characteristics, such as a decrease in the S/Nratio, together with an increase in the signal charge accumulation time.

Naturally the present invention is not limited to the foregoingembodiments and descriptions but is subject to various modifications andcombinations within the scope and spirit of the appended claims.

What is claimed is:
 1. A drive method for a photoelectric conversiondevice for reading signals in succession from plural photoelectricconverting elements, arranged two-dimensionally on a substrate, bysuccessively scanning drive lines in the X-direction therebytransferring signals charges along signal lines in the Y-direction,which comprises:scanning in succession only arbitrarily selected drivelines for said plural photoelectric converting elements, and driving atleast plural of the remaining drive lines not arbitrarily selectedsimultaneously for signal transfer at a timing different from the timingof drive of said arbitrarily selected drive lines for discharging asignal charge based on an image information by photoelectric conversionin the photoelectric converting elements as unnecessary information. 2.A drive method for a photoelectric conversion device according to claim1, wherein potentials at both ends of said photoelectric convertingelements with said remaining drive lines are simultaneously returned toinitial values.
 3. A drive method for a photoelectric conversion deviceaccording to claim 1, wherein said remaining drive lines arecollectively driven.
 4. A drive method for a photoelectric conversiondevice according to claim 1, wherein said remaining drive lines aredriven in divided manner.
 5. A drive method for a photoelectricconversion device according to claim 1, wherein, after transferringsignal charges obtained by photoelectric conversion in the photoelectricconverting elements corresponding to said arbitrarily selected drivelines, the drive lines are so driven as to initialize all thephotoelectric converting elements.
 6. A drive method for a photoelectricconversion device according to claim 1, including a mode for readingsignals by driving said arbitrarily selected drive lines, and a mode forreading signals by driving arbitrarily selected second drive linesdifferent from the aforementioned arbitrarily selected drive lines.
 7. Adrive method for a photoelectric conversion device according to claim 6,wherein said two modes are executed alternately.
 8. A drive method for aphotoelectric conversion device according to claim 1, wherein saidarbitrarily selected drive lines are selected by a plural number, anddriven in succession from one at an inner side of the selected ones toone at an outer side thereof.
 9. A drive method for a photoelectricconversion device according to claim 8, wherein said arbitrarilyselected drive lines are selected by a plural number and driven, priorto the reading of the signal charges by said drive lines, forinitialization in succession from one at an inner side of the selectedones to one at an outer side thereof.
 10. A drive method for aphotoelectric conversion device according to claim 1, wherein saidarbitrarily selected drive lines are selected by a plural number, anddriven, prior to the reading of the signal charges by said drive lines,for initialization in succession from one at an inner side of theselected ones to one at an outer side thereof.
 11. A photoelectricconversion device for reading signals in succession from pluralphotoelectric converting elements, arranged two-dimensionally on asubstrate, by successively scanning drive lines in the X-directionthereby transferring signals charges along signal lines in theY-direction, comprising:means for successively scanning arbitrarilyselected ones only among drive lines for said plural photoelectricconverting elements; and means for driving at least plural of theremaining drive lines not arbitrarily selected simultaneously at atiming different from the timing of drive of said arbitrarily selecteddrive lines for discharging a signal charge from the photoelectricconverting elements as unnecessary information.
 12. A photoelectricconversion device according to claim 11, wherein said photoelectricconverting element comprises in succession:a first electrode layer; afirst insulation layer for inhibiting the passing of both the carriersof a first type and the carriers of a second type, different in polarityfrom those of said first type; an amorphous photoelectric convertingsemiconductor layer; a second electrode layer; and an injectioninhibiting layer positioned between said second electrode layer and saidphotoelectric converting semiconductor layer and adapted to inhibit theinjection of the carriers of the first type into said photoelectricconverting semiconductor layer.
 13. A photoelectric conversion deviceaccording to claim 11, wherein said photoelectric converting elementincludes a power supply unit, a detection unit and a control unit forcontrolling the switch element in such a manner;in a refreshing mode, asto apply an electric field to the layers of said photoelectricconverting element in such a direction as to guide the carriers of saidfirst type from said photoelectric converting semiconductor layer tosaid second electrode layer; in a photoelectric conversion mode, as toapply an electric field to the layers of said photoelectric convertingelement in such a direction as to retain the carriers of said firsttype, generated by the light entering said photoelectric convertingsemiconductor layer, in said photoelectric converting semiconductorlayer, and to guide the carriers of said second type to said secondelectrode layer, and thereby detecting, as a light-induced signal, thecarriers of said first type accumulated in said photoelectric convertingsemiconductor layer or the carriers of said second type guided to saidsecond electrode layer in said photoelectric conversion mode.
 14. Aphotoelectric conversion device according to claim 13, wherein:saidswitch element includes a gate electrode layer; a second insulationlayer; a non-single crystalline semiconductor layer; first and secondelectrode layers formed as a pair across a portion, constituting achannel area, of said semiconductor layer; and an ohmic contact layerprovided between said main electrode layers and said semiconductorlayer.
 15. A photoelectric conversion device according to claim 13,wherein:said switch element includes a gate electrode layer; a secondinsulation layer; a non-single crystalline semiconductor layer; firstand second electrode layers formed as a pair across a portion,constituting a channel area, of said semiconductor layer; and an ohmiccontact layer provided between said main electrode layers and saidsemiconductor layer, and said first electrode layer and said gateelectrode layer; said first insulation layer and said second insulationlayer; said photoelectric converting semiconductor layer and saidsemiconductor layer; said second electrode layer and said main electrodelayer; and said injection inhibiting layer and said ohmic contact layer;are constituted respectively by common films.
 16. A photoelectricconversion device according to claim 13, wherein:said switch elementincludes a gate electrode layer; a second insulation layer; a non-singlecrystalline semiconductor layer; first and second electrode layersformed as a pair across a portion, constituting a channel area, of saidsemiconductor layer; and an ohmic contact layer provided between saidmain electrode layers and said semiconductor layer, and wherein at leasta part of said photoelectric converting semiconductor layer and saidsemiconductor layer is constituted by hydrogenated amorphous silicon.17. A photoelectric conversion device according to claim 11, furthercomprising switching means for switching a state for obtaining signalsfrom all of said plural photoelectric converting elements and a statefor obtaining signals from said arbitrarily selected portion.
 18. Aphotoelectric conversion device according to claim 11, furthercomprising a fluorescent member on said photoelectric convertingelements.
 19. A photoelectric conversion device for reading signals insuccession from plural photoelectric converting elements, arrangedtwo-dimensionally on a substrate, by successively scanning drive linesin the X-direction thereby transferring signals charles along signallines in the Y-direction, comprising:means for successively scanningarbitrarily selected ones only among drive lines for said pluralphotoelectric converting elements; wherein said photoelectric convertingelement comprises in succession; a first electrode layer; a firstinsulation layer for inhibiting the passing of both the carriers of afirst type and the carriers of a second type, different in polarity fromthose of said first type; an amorphous photoelectric convertingsemiconductor layer; a second electrode layer; and an injectioninhibiting layer positioned between said second electrode layer and saidphotoelectric converting semiconductor layer and adapted to inhibit theinjection of the carriers of the first type into said photoelectricconverting semiconductor layer.
 20. A photoelectric conversion deviceaccording to claim 19, wherein said photoelectric converting elementincludes a power supply unit, a detection unit and a control unit forcontrolling the switch element in such a manner;in a refreshing mode, asto apply an electric field to the layers of said photoelectricconverting element in such a direction as to guide the carriers of saidfirst type from said photoelectric converting semiconductor layer tosaid second electrode layer; in a photoelectric conversion mode, as toapply an electric field to the layers of said photoelectric convertingelement in such a direction as to retain the carriers of said firsttype, generated by the light entering said photoelectric convertingsemiconductor layer, in said photoelectric converting semiconductorlayer, and to guide the carriers of said second type to said secondelectrode layer, and thereby detecting, as a light-induced signal, thecarriers of said first type accumulated in said photoelectric convertingsemiconductor layer or the carriers of said second type guided to saidsecond electrode layer in said photoelectric conversion mode.
 21. Aphotoelectric conversion device according to claim 20, wherein:saidswitch element includes a gate electrode layer; a second insulationlayer; a non-single crystalline semiconductor layer; first and secondelectrode layers formed as a pair across a portion, constituting achannel area, of said semiconductor layer; and an ohmic contact layerprovided between said main electrode layers and said semiconductorlayer.
 22. A photoelectric conversion device according to claim 21,wherein:said first electrode layer and said gate electrode layer; saidfirst insulation layer and said second insulation layer; saidphotoelectric converting semiconductor layer and said semiconductorlayer; said second electrode layer and said main electrode layer; andsaid injection inhibiting layer and said ohmic contact layer;areconstituted respectively by common films.
 23. A photoelectric conversiondevice according to claim 20, wherein at least a part of saidphotoelectric converting semiconductor layer and said semiconductorlayer is constituted by hydrogenated amorphous silicon.
 24. Aphotoelectric conversion device according to claim 19, furthercomprising switching means for switching a state for obtaining signalsfrom all of said plural photoelectric converting elements and a statefor obtaining signals from said arbitrarily selected portion.
 25. Aphotoelectric conversion device according to claim 19, furthercomprising a fluorescent member on said photoelectric convertingelements.